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drk answered: 1901 problems
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test/255374: The sum of the squares of two consecutive odd positive integers is 202. Find the integers.
1 solutions

Answer 187643 by drk(1908) About Me  on 2010-01-10 14:58:22 (Show Source):
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let x = positive odd integer and x + 2 be the next positive odd integer.
we get
x^2 + (x+2)^2 = 202
foiling the left and combining like terms, we get
2x^2 + 4x + 4 = 202
and then
2x^2 + 4x - 198 = 0
divide by 2 to get
x^2 + 2x - 99 = 0
factor to get
(x+11)(x-9) = 0
solving for x, we get
x = -11 and x = 9
we get (-11,-9) OR (9,11)


Probability-and-statistics/255362: The probability that an American CEO can transact business in a foreign language is .20. Ten
American CEOs are chosen at random. (a) What is the probability that none can transact business
in a foreign language? (b) That at least two can? (c) That all 10 can? (d) Sketch the probability
distribution and discuss its appearance.
1 solutions

Answer 187640 by drk(1908) About Me  on 2010-01-10 14:53:17 (Show Source):
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P(speak foreign language) = .20
P(NOT speak foreign language) = .80
(a) What is the probability that none can transact business in a foreign language?
answer: we want zero "YES" and 10 "NO" so,
nCr*(no)^10*(yes)^0
or
10c0*.8^10*.2^0 ~ .1074
--
(b) That at least two can?
answer: This means that 0 or 1 cannot. It is easier to do this in negation.
1 - p(0 not) + p(1 not) = 1 - 10c0(.8)^0*(.2)^10 + 10c1*(.8)^1*(.2)^9 ~ .99999
--
(c) That all 10 can?
answer; we want all 10 yes, so,
10c10*(.2)^10 ~ 1.02 x 10^-7
(d) Sketch the probability distribution and discuss its appearance.
The sketch should be a normal curve with cum sum = 1.


Human-and-algebraic-language/255365: What is the slope of a line that is perpendicular to a line that has no slope? Explain the answer.
1 solutions

Answer 187634 by drk(1908) About Me  on 2010-01-10 14:40:55 (Show Source):
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If a line has no slope then it can be expressed as 1/0 or in general as a/0, where a not = 0.
A perpendicular slope is the negative reciprocal.
So, 1/0 turns into -0/1 = 0,
or in general a/0 turns into -0/a = 0.


Human-and-algebraic-language/255369: what is the unit rate of change of y with respect to x if the slope of the graph of the equation for y in terms of x is 1/4?
1 solutions

Answer 187633 by drk(1908) About Me  on 2010-01-10 14:38:53 (Show Source):
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For every 1 increase in y, we increase x by 4.
unit rate of change of y with respect to x = rise information over run information.


Quadratic_Equations/255366: (x*-3x)+8=0
cant figure out how to do the last part of question after I get here
x= 3 + - square root -23 over 2
1 solutions

Answer 187632 by drk(1908) About Me  on 2010-01-10 14:37:33 (Show Source):
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Your original equation was:
%28x%2A-3x%29%2B8=0
suppose * = 2. then we have a quadratic of the form
%28x2-3x%29%2B8=0
which can easily be solved using the quadratic formula as
x+=+%283+%2B-+sqrt%28+9-4%2A1%2A8+%29%29%2F%282%2A1%29+
which is simplified as
x+=+%283+%2B-+sqrt%28-23%29%29%2F2+
From here you have one of two ways to go.
(1) if you have never been shown imaginary numbers, then say no solution.
(2) If you have been shown imaginary numbers, then say
%283+%2B+isqrt%2823%29%29%2F2 , %283+-+isqrt%2823%29%29%2F2


Exponents/255363: please help me solve this problem... 4^x=(1/2)^3x+5
1 solutions

Answer 187630 by drk(1908) About Me  on 2010-01-10 14:33:05 (Show Source):
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If you mean
4%5Ex=%281%2F2%29%5E%283x%29%2B5, then
simplify as
4%5Ex+=+%281%2F8%29%5Ex+%2B+5.
multiplying both sides by 8^x, we get
32%5Ex+=+x+%2B+5%2A8%5Ex
in this case, there is no x value which is true.
--
If you mean
4%5Ex=%28%281%2F2%29%5E3%29x%2B5
simplifies as
4%5Ex=%281%2F8%29x%2B5.
Multiply both sides by 8 to get
8%2A4%5Ex=x%2B5
In this case, there is no x value which is true.
--
If you mean
4%5Ex=%281%2F2%29%5E%283x%2B5%29
then rewrite the right side as
4%5Ex+=+2%5E%28-3x-5%29
the 4 can be expressed as 2^2, so we get
2%5E%282x%29+=+2%5E%28-3x-5%29
cancel the base 2's to get
2x+=+-3x-5
solve for x to get
x+=+-1


Angles/255357: The measure of the supplement of an angle exceeds three times the measure of half the compliment of the angle by 12. Find the measure of half the supplement
1 solutions

Answer 187625 by drk(1908) About Me  on 2010-01-10 14:20:04 (Show Source):
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Let x be an angle.
180-x is the supplement.
90 - x is the compliment.
So, we get
180-x+=+3%2A%281%2F2%29%2A%2890-x%29+%2B+12
By distributive prperty, we get
180-x+=+135+-+%283%2F2%29%29x+%2B+12
combining like terms on the right we get
180-x+=+147+-+%283%2F2%29x
and simplifying we get
33+=+%281%2F2%29x
66+=+x
The supplement of 66 is 114. Half of 114 is 57.
So answer is 57.


Graphs/255361: how do i write an equation in slope-intercept form for the lone that is perpendicular to the given lone and passes through the given point
y=-3x+4;(6,-2)
1 solutions

Answer 187624 by drk(1908) About Me  on 2010-01-10 14:15:41 (Show Source):
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step 1 - solve the equation for y. That is already done and given as
(i) y+=+3x+%2B+4
step 2 - find the slope of (i) and we get m = 3.
step 3 find perpendicular slope. m = 3, so perpendicular means flip and change sign. Perp m = -1/3.
step 4 - using new slope and (6,-2) we put that information into
y=mx%2B+bto get
-2+=+%28-1%2F3%29%2A6+%2B+b
-2+=+-2+%2B+b
b+=+0
step 5 - write the answer as
y+=+%28-1%2F3%29x+%2B+0


Equations/255360: (4.2y)/0.2-84=y
1 solutions

Answer 187623 by drk(1908) About Me  on 2010-01-10 14:12:28 (Show Source):
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%284.2y%29%2F0.2-84=y
step 1 - divide 4.2 by .2 to get
21y+-+84+=+y
step 2 - subtract 21y from both sides to get
-84+=+-20y
step 3 - divide by -20 to get
4.2+=+y


Equations/255356: 25n-(-15n-4)=28n
1 solutions

Answer 187622 by drk(1908) About Me  on 2010-01-10 14:09:54 (Show Source):
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25n-%28-15n-4%29=28n
step 1 - distribute the negative through to get
25n+%2B+15n+%2B+4+=+28n
step 2 - combine like terms on the left to get
40n+%2B+4+=+28n
step 3 - subtract 40n from both sides to get
4+=+-12n
step 4 - divide to get
n+=+-1%2F3


Travel_Word_Problems/255359: Two airplanes start toward each other at the same time from airports located 1950 km apart. One plane flies at an average speed of 360 km/h. What should the average speed of the plane be if they meet in 3 hours? Show all work.
1 solutions

Answer 187621 by drk(1908) About Me  on 2010-01-10 14:07:29 (Show Source):
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This is a RTD problem. Here is the table based on given information:
airplane . . . . . . . . .rate . . . . . . . . .time . . . . . . . . .distance
A . . . . . . . . . . .. . . .360 . . . . . . . . .3 . . . . .. . . . . .. . 1080
B . . . . . . . . . . . . . . .R . . . . . . . . . . .3 . . . . . . .. . . . .. . 3R
totals . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1950
The distance of A + distance of B = total distance. So,
1080 + 3R = 1950
3R = 870
R = 290 km/h


Functions/255355: write in standard form, m= 5 and b = -5
1 solutions

Answer 187620 by drk(1908) About Me  on 2010-01-10 14:03:23 (Show Source):
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Lets start with slope intercept form as
y+=+mx+%2B+b
we know m = 5 and b = -5, so we get
(i) y+=+5x-5
standard form requires 2 things
(1) no decimals
(2) X and Y stuff on the same side and the # by itself.
From (i) subtract 5x to get
(ii) -5x+%2B+y+=+-5
This is standard form.


Word_Problems_With_Coins/255358: You have two U.S. coins with a total value of $.35, and one of them is not a quarter. What are the coins?
1 solutions

Answer 187619 by drk(1908) About Me  on 2010-01-10 14:00:52 (Show Source):
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This is a trick question. If one cannot be a quarter, the other one CAN be a quarter. So, we have dime and then quarter.


Equations/255352: how do you write 5580 in scientific notation.
1 solutions

Answer 187618 by drk(1908) About Me  on 2010-01-10 13:59:54 (Show Source):
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Notice there is no decimal. IF you don't see one, it is all the way to the right. We want a number expressed in the following form:
a%2A10%5Eb
where 0 < a < 10 and b is an integer.
step 1 - move the decimal left 3 jumps to get
5.580
step 2 - ask yourself how many jumps and in which direction?
# jumps = 3
direction = left
OUr answer is:
5.580 x 10^3


Rational-functions/255299: solve using the rational zero theorem and descarte rule:x^4-5x^3-54x^2-80x-32=0
1 solutions

Answer 187617 by drk(1908) About Me  on 2010-01-10 13:54:51 (Show Source):
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x^4 - 5x^3 - 54x^2 - 80x - 32 = 0
step 1 - set up P, N, i
P are the number of sign changes you see when (x) is placed into the equation. We get P = 1.
N are the number of sign changes you see when (-x) is placed into the equation. We get N = 3.
Now 1 + 3 = 4.
P . . . 1 . . . . 1
N . . . 3 . . . . 1
i . . . .0 . . . . .2
Notice that i = 0 or 2. Imaginary numbers always travel in conjugate pairs.
Now on to rational zeros. or P/Q
P = +-(1, 2, 4, 8, 16, 32)
Q = +-(1)
We can find that x = -4 and x = -1 give us 2 zeros.
By synthetic division, using x = -4, we get
(x^3-9x^2-18x-8)
and this divided by x = -1 gets us
(x^2-10x-8)
setting this = 0 and solving gets us
x+=+%2810+%2B-+sqrt%28+100-4%2A1%2A%28-8%29+%29%29%2F%282%29+
or
x+=+%2810+%2B-+sqrt%28+132+%29%29%2F%282%29+
or simplified as
x+=+%285+%2B-+sqrt%28+33%29%29+
SO our four answers are:
x = -4, x = -1, x = 5 +-sqrt(33)


Graphs/255314: Flying against the wind, a plane makes a 1050km trip in 3.5 hours. On the return trip, the flight takes 30 minutes less. What is the rate of the plane in calm air?
1 solutions

Answer 187591 by drk(1908) About Me  on 2010-01-10 12:11:30 (Show Source):
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This is an rtd problem with currents. Here is a table based on the given information:
plane . . . . . .rate . . . . . . . . . . . time . . . . .distance
against . . . .r-c=1050 . . . . . . . .3.5 . . . . . . 3675
with . . . . . .r+c . . . . . . . . .. . . .. 3 . . .. . . . .3675
we know
(i) r-c = 1050.
solve with for r+c, we get
(ii) r+c = 1225
adding (i) and (ii) together, we get
(iii) 2r = 2275
r = 1137.5
c then is 87.5 Kph


Linear-equations/255303: ((x^2 - x) / (x^2 + 3x + 2)) / ((x^2 + 2x)/ (x^2 -1))
or
http://www.thea.nesinc.com/images/math/tasp_image335.gif
1 solutions

Answer 187590 by drk(1908) About Me  on 2010-01-10 12:06:45 (Show Source):
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OUr expression is:

step 1 - factor each part separately:
x^2-x = x(x-1)
x^2 + 3x + 2 = (x+2)(x+1)
x^2+ 2x = x(x+2)
x^2-1 = (x+1)(x-1)
we get
%28x%2A%28x-1%29%29%2F%28%28x%2B2%29%28x%2B1%29%29 / %28x%2A%28x%2B2%29%29%2F%28%28x%2B1%29%28x-1%29%29
step 2-Multiply the top fraction by the reciprocal of the bottom fraction to get
%28x%2A%28x-1%29%29%2F%28%28x%2B2%29%28x%2B1%29%29 * %28%28x%2B1%29%28x-1%29%29%2F%28x%2A%28x%2B2%29%29
step 3 - cancel where possible to get
%28x-1%29%5E2+%2F+%28x%2B2%29%5E2


Linear-equations/255309: how do you find the slope of a line when your only given two points? we are required to solve it algebralicly with out graphing. i know that there is an equation to solve it but im not sure what it is or how it works.
1 solutions

Answer 187588 by drk(1908) About Me  on 2010-01-10 11:59:49 (Show Source):
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Suppose you are given 2 coordinates: A (x1,y1) and B (x2,y2). We can find the slope with the dollowing equation:
m+=+%28y2-y1%29%2F%28x2-x1%29
--
EX: A(1,4) B (-3,9)
using the slope formula we get
m+=+%289-4%29%2F%28-3-1%29 = 5/-4
so
m = -5/4


Polynomials-and-rational-expressions/255307: ((C+5)/7)+((C-30)/4)=5/14
I KEEP COMING UP WITH BIG NUMBERS EVEN THOUGHT THE SOLUTION IS SUPPOSED TO BE "1"
1 solutions

Answer 187587 by drk(1908) About Me  on 2010-01-10 11:57:09 (Show Source):
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%28%28C%2B5%29%2F7%29%2B%28%28C-30%29%2F4%29=5%2F14
step 1 - find the common denominator. It is 28.
step 2 - multiply every number by 28 to get
4%2A%28C%2B5%29%2B7%2A%28C-30%29=2%2A5
and then
4C+%2B+20++%2B+7C+-+210+=+10
step 3 - combine like terms on the left to get
11C++-+190+=+10
add 190 to both sides to get
11C++-+190+=+10
11C+=+200
c= 18.1818....
--
checking, we get
%28%2818.1818%2B5%29%2F7%29%2B%28%2818.1818-30%29%2F4%29=5%2F14
%28%2823.1818%29%2F7%29%2B%28%28-12.1818%29%2F4%29=5%2F14
3.3116 - 2.9545 ~ .357054 ; 5/14 = .3571428


Inequalities/255281: n is an integer
a) Write down the values of n which satisfy the inequality
-2 < n ≤ 3
b) Solve the inequality
3x + 2 ≤ 4


Thanks everyone :D
1 solutions

Answer 187559 by drk(1908) About Me  on 2010-01-10 09:47:50 (Show Source):
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(a) the values of n are: -1, 0, 1, 2, and 3. We can't use -2 because it is not =.
(b) 3x + 2 ≤ 4
step 1 - subtract 2 to get
3x <=2
step 2 - divide by 3 to get
x<= 2/3
If you want the set of integers then
(- 00, 0]


Miscellaneous_Word_Problems/255273: A staircase has 5 steps. You can walk up the staircase by taking one or two steps at a time. How many different ways can you walk up the staircase?


1 solutions

Answer 187552 by drk(1908) About Me  on 2010-01-10 09:16:14 (Show Source):
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we have
1,1,1,1,1
1,1,1,2
1,1,2,1
1,2,1,1
2,1,1,1
1,2,2
2,1,2
2,2,1
so, it appears we have 8 ways


Numbers_Word_Problems/255261: show that (x+2)squared(x-2)squared is equal to x to the fourth-8x squared + 16?
1 solutions

Answer 187551 by drk(1908) About Me  on 2010-01-10 09:14:21 (Show Source):
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%28x%2B2%29%5E2%2A%28x-2%29%5E2
this is the same as
%28%28x%2B2%29%28x-2%29%29%5E2
now (x+2)(x-2) = x^2-4, so we get
%28x%5E2-4%29%5E2
squaring this gets us
x%5E4+-+8x%5E2+%2B16


Miscellaneous_Word_Problems/255259: What is the largest positive integer k so that 5k divides 26!?

1 solutions

Answer 187549 by drk(1908) About Me  on 2010-01-10 09:10:47 (Show Source):
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Part of 26! are the numbers: 5, 10, 15, 20, and 25.
5*1 = 5
5*2 = 10
5*3 = 15
5*4 = 20
5*5 = 25
factor out the 5's from the left and we have
5(1*2*3*4*5)
or 5*120.
So, k = 120


Geometric_formulas/255276: A circular archery target is 122 cm in diameter and consists of a bull's eye of diameter 12.2 cm, surrounded by nine evenly spaced concentric circles. Assume that an arrow that hits a target is equally likely to land anywhere on the target. What's the probability that the arrow will A) hit the bulls eye B) Land somewhere in the outmost four circles. C) Land within the fifth ring in from the outer edge. ---Please help on this problem! THANKS!
1 solutions

Answer 187548 by drk(1908) About Me  on 2010-01-10 09:07:44 (Show Source):
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Let's call the bulls eye - circle 1 including circle #1, there are 10 concentric circles.
radius of circle 1 = 6.1
radius of circle 2 = 12.2 or 6.1 * 2.
and so on.
A) hit the bulls eye
P(bulls eye) = pi*6.1^2 = 37.21pi cm^2
B) Land somewhere in the outmost four circles.
P(outer 4 circles) = p(whole target - inner 6 circles) = pi*R^2 - pi*r^2 = pi*61^2 -pi*36.6^2.
The 36.6 is the radius of the first 6 circles or 6.1 * 6.
This gives us 2381.44pi cm^2
C) Land within the fifth ring in from the outer edge.
P(5th ring) = p(5th ring - p(4th ring). We want only the fifth ring so all other inner rings must be subtracted out. We get pi*R^2 - pi*r^2 = pi*30.5^2 -pi*24.4^2 = 334.89pi cm^2


Rectangles/255278: The length of a rectangle is x + 4
The width of a rectangle is x - 1
The perimeter is 46 cm
Calculate the length of the diagonal of the rectangle

Please help?!
1 solutions

Answer 187546 by drk(1908) About Me  on 2010-01-10 08:57:30 (Show Source):
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The length of a rectangle is x + 4
The width of a rectangle is x - 1
The perimeter is 46 cm
--
We can use th perimter formula as:
(i)P+=+2L+%2B+2W
replacing x + 4 for L, x - 1 for W, and 46 for P, we get
(ii) 46+=+2%28x%2B4%29+%2B+2%28x-1%29
we solve for x as
(iii) 46+=+2x+%2B+8+%2B+2x+-+2
(iv) 46+=+4x+%2B+6
(v) 40+=+4x
(vi) 10+=+x
Now, the length = 14, and the width is 9.
--
Using the Pythagorean theorem:
a%5E2+%2B+b%5E2+%2B+c%5E2
we get
14%5E2+%2B+9%5E2+=+c%5E2
196+%2B+81+=+c%5E2
277+=+c%5E2
the diagonal, c, ~ 16.64


Trigonometry-basics/255277: Simplify:
(sec^2xcscx)/(sec^2x + csc^2x)
1 solutions

Answer 187545 by drk(1908) About Me  on 2010-01-10 08:52:15 (Show Source):
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Simplify
(i) %28sec%5E2%28x%29%2Acsc%28x%29%29%2F%28sec%5E2%28x%29+%2B+csc%5E2%28x%29%29
turn everything into sin and cos as
(ii)
simplify the denominator to get
(iii)
Notice cos^2x + sin^2 x = 1. Multiply by the reciprocal to get
(iv) %28cos%5E2%28x%29%2Asin%5E2%28x%29%29%2F%28cos%5E2%28x%29%2Asin%28x%29%29
and simply
(v) sin%28x%29


Rectangles/255275: A rectangle has a width of 10 inches and an area of 5 square inches. what is the length of the rectangle?
1 solutions

Answer 187542 by drk(1908) About Me  on 2010-01-10 08:43:56 (Show Source):
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We have 1 formula:
(i) A = L x W
step 1 - replace A = 5 and W = 10 to get
(ii) 5 = 10L
step 2 - divide by 10 to get
(iii) 1/2 = L
Length = 1/2 in.


Parallelograms/255124: How do you find the perimeter of a parallelogram when you have the base of 4m, height of 3m and don't have side length?
1 solutions

Answer 187438 by drk(1908) About Me  on 2010-01-09 15:22:14 (Show Source):
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I assume it is isosceles. We can use Pythagorean theorem
a^2 + b^2 = c^2
and then
3^3 + 4^2 = c^2
9 + 16 = c^2
25 = c^2
5 = c.
The perimeter is 3 + 4 + 5 + 5 = 17 m.


real-numbers/255128: Is 3 over pie an irrational number?
1 solutions

Answer 187437 by drk(1908) About Me  on 2010-01-09 15:20:21 (Show Source):
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Yes, since PI is irrational, a rational / irrational is irrational.


Equations/254924: A= 1/2h (a+b) for b
1 solutions

Answer 187282 by drk(1908) About Me  on 2010-01-08 19:48:06 (Show Source):
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A= 1/2h (a+b) for b.
step 1 - multiply both sides by 2 to get
2A+=+h%28a%2Bb%29
step 2 - divide by h to get
2A%2Fh+=+a%2Bb
subtract a to get
2A%2Fh+-+a+=+b


Square-cubic-other-roots/254941: Solve for n: cube root of (n + 9) - cube root of (n - 9) = 3
1 solutions

Answer 187277 by drk(1908) About Me  on 2010-01-08 19:36:29 (Show Source):
You can put this solution on YOUR website!
%28n+%2B+9%29%5E%281%2F3%29+-+%28n+-+9%29%5E%281%2F3%29+=+3
To solve this via algebraic means may get messy, but the answer is rather simple:
n = 4sqrt(5)