New!
Get regular updates about newly solved problems
via algebra.com's RSS system.
Recent problems solved by 'drk'
drk answered: 1901 problems
Jump to solutions: 0..29 , 30..59 , 60..89 , 90..119 , 120..149 , 150..179 , 180..209 , 210..239 , 240..269 , 270..299 , 300..329 , 330..359 , 360..389 , 390..419 , 420..449 , 450..479 , 480..509 , 510..539 , 540..569 , 570..599 , 600..629 , 630..659 , 660..689 , 690..719 , 720..749 , 750..779 , 780..809 , 810..839 , 840..869 , 870..899 , 900..929 , 930..959 , 960..989 , 990..1019 , 1020..1049 , 1050..1079 , 1080..1109 , 1110..1139 , 1140..1169 , 1170..1199 , 1200..1229 , 1230..1259 , 1260..1289 , 1290..1319 , 1320..1349 , 1350..1379 , 1380..1409 , 1410..1439 , 1440..1469 , 1470..1499 , 1500..1529 , 1530..1559 , 1560..1589 , 1590..1619 , 1620..1649 , 1650..1679 , 1680..1709 , 1710..1739 , 1740..1769 , 1770..1799 , 1800..1829 , 1830..1859 , 1860..1889 , 1890..1919, >>Next
test/266674: the equation of a tangent line to the curve x^2+y^2=169 at the point (5,-12) is? 1 solutions
Answer 195914 by drk(1908) on 2010-02-07 14:39:54 (Show Source):
You can put this solution on YOUR website!step 1 - we take a derivative of both sides and get

step 2 - solve for dy/dx

step 3 - put your coordinates in and get

---
so, the slope is
dy/dx = m = 5/12
---
step 4 - using slope and our coordinate as well as y = mx + b, we get

and then

solving for b, we get

---
step 5 - final equation is
|
Geometry_Word_Problems/266668: You have 700 feet of fencing to enclose a rectangular field. Express the area of the field, A, as a function of one of its dimensions, x. 1 solutions
Answer 195913 by drk(1908) on 2010-02-07 14:32:47 (Show Source):
You can put this solution on YOUR website!The perimeter is expressed as
(i) 
or
(ii) 
dividing by 2 we get
(iii) 
solve for y as
(iv) 
---
area formula is
(v) 
substituting (iv) into (v) we get
(vi)
|
Length-and-distance/266670: Find the coordinates of the other endpoint of the segment, given its midpoint and one endpoint.
Midpoint (8,0), endpoint (3,2)
The other endpoint is......? (must have ordered pair) 1 solutions
Answer 195912 by drk(1908) on 2010-02-07 14:30:15 (Show Source):
You can put this solution on YOUR website!Line them up like this
endpoint: (3,2)
midpoint: (8,0)
endpoint:
to find the endpoint coordinates,
look at the x's. 3 to 8 means add 5. add 5 more and we get 13
look at the y's. 2 to 0 means subtract 2. subtract 2 more and we get -2.
The other endpoint is
(13,-2)
|
Trigonometry-basics/266671: SKATEBOARDING The angle that a skateboarding ramp forms with the ground is 25 degrees and the height of the ramp is 6 feet. Determine the length of the ramp. 1 solutions
Answer 195910 by drk(1908) on 2010-02-07 14:27:47 (Show Source):
You can put this solution on YOUR website!draw a right triangle and place 25 degrees at a bottom vertex
in this case we have the opposite side and want the hypotenuse. This means we need sine theta.
sin 25 = 6/r
r = 6/sin(25) ~ 14.2 feet
|
Surface-area/266666: 1.What is the surface area that has a diameter of 3 inches and height of 5 inches?
2.What is the total square feet of a rectangle that is 12 ft x 8ft x11ft?
3.A rectangular swimming pool has a length of 18 ft, width of 10 ft, and a depth of 4ft. What is the volume of water the pool can hold? 1 solutions
Answer 195907 by drk(1908) on 2010-02-07 14:23:33 (Show Source):
You can put this solution on YOUR website!1.What is the surface area that has a diameter of 3 inches and height of 5 inches?

the diameter = 3, so radius = 1.5

so

or

---
2.What is the total square feet of a rectangle that is 12 ft x 8ft x11ft?

we get

then
 or 
---
3.A rectangular swimming pool has a length of 18 ft, width of 10 ft, and a depth of 4ft. What is the volume of water the pool can hold?

or

which is
 cu. ft.
|
test/266664: if x+y=xy, then dy/dx is? 1 solutions
Answer 195904 by drk(1908) on 2010-02-07 14:16:56 (Show Source):
You can put this solution on YOUR website!We use implicit differentiation here. On the left, it is regular derivatives, but on the right we need to the product rule. we get
(i) 
step 1 - subtract 1 (dy/dx) from both sides and then subtract y from both sides to get
(ii) 
step 2 - factor out the dy/dx to get
(iii) 
step 3 - divide by x-1 to get
(iv)
|
Miscellaneous_Word_Problems/266657: Oh please help me, this problem has almost made me cry. I am a 34 year old student and can't even begin to understand this..
A mini license plate for a toy car must consist of a number followed by two letters. Each letter must be a C, A, or R. Each number must be a 3 or 7. Repetitions of letters is permitted.
there are 4 parts to this:
1. Use the counting principle to determine the number of points in the sample space.
2. Construct a tree diagram to represent this situation.
3. List the sample space.
4. Determine the EXACT probability of creating a mini license plate with a C. Give the solution in reduced fraction form.
Please show me everything, I have 7 other problems to do like this and I need alot of help please, I am taking online courses and my professor isn't helping much at all. 1 solutions
Answer 195902 by drk(1908) on 2010-02-07 14:12:59 (Show Source):
You can put this solution on YOUR website!First our license plate must be in the form of
# - L - L,
or,
number - letter - letter.
we have 2 choices for the numbers, 3 or 7
we have 3 choices for the letters c - a - r.
repetition is allowed: So there is a second 3 choices for letters c - a - r
---
1. Use the counting principle to determine the number of points in the sample space.
ANSWER: The counting principal is all about multiplying the number of ways one event occurs x the number of ways a second event occurs x the number of ways a third event occurs and so on. In our case we have 2 number choices and 3 letter choices, but two times.
2 x 3 x 3 = 18.
---
2. Construct a tree diagram to represent this situation.
ANSWER:
step 1 - write a 3 and below it with a little space write a 7
step 2 - from the 3 draw 3 arrows and next to the end of these write c, a, r
step 3 - next to each of the letters draw another 3 arrows and write the letters again for c, a, r
step 4 - from the 7 draw 3 arrows and next to the end of these write c, a, r
step 5 - next to each of the letters draw another 3 arrows and write the letters again for c, a, r
---
3. List the sample space.
ANSWER: this is pretty straight forward from the tree diagram. we get
3aa, 3ab, 3ac, 3ba, 3bb, 3bc, 3ca, 3cb, 3cc,
7aa, 7ab, 7ac, 7ba, 7bb, 7bc, 7ca, 7cb, 7cc.
3ab plate is different from 3ba plate
---
4. Determine the EXACT probability of creating a mini license plate with a C. Give the solution in reduced fraction form.
ANSWER: 3ac, 3bc, 3cc, 3ca, 3cb, 7ac, 7bc, 7cc, 7ca, 7cb
"with a C" means to me one or two C"s in any order.
P(C) = 10/18 = 5/9.
|
Surface-area/266652: Suppose the volume must be 50in^3, What are the values for r and h that will minimize the amount of sheet metal required to obtain this volume. I know volume is v= (pi)r^2h. I also know the surface area is sa= 2(pi)rh+2(pi)r^2.
I have been working on this all day. Any help would be greatly appreciated. Thanks 1 solutions
Answer 195898 by drk(1908) on 2010-02-07 13:57:40 (Show Source):
You can put this solution on YOUR website!lets start with
(i) 
we know v = 50, so we get
(ii) 
If we solve for h, we get
(iii) 
now we look at surface area as
(iv) 
substitute (iii) into (iv) to get
(v) 
now everything is in terms of r.
getting a common denominator as pir^2, we get
(vi) 
now, factoring, we get
(vii) 
reducing we get
(viii) 
It turns out that r is minimum at 2.
This means that h = 50/4pi or h ~ 3.97887
This gives us a minimum sa at
sa = 75.1326
|
Linear-systems/266647: please this the last time i am asking for help.
solve for x and y.
during a techno-geek-store sale 6 blank video tapes and 12 blank dvd's cost $35.10.during the same sale, 8 blank video tapes and 3 blank dvd's cost $27.95. what was the cost of a blank video tape and the cost of a blank dvd?
please!please!please!help me!!! 1 solutions
Answer 195891 by drk(1908) on 2010-02-07 13:35:57 (Show Source):
You can put this solution on YOUR website!Let v = video and d = dvd
---
from the given we get
(i) 
(ii) 
step 1 - multiply (ii) by -4 to get
(iii) 
step 2 - add (ii) and (iii) to get
(iv) 
divide by -26 to get
(v) 
and then
(vi)
|
Geometry_Word_Problems/266645: a triangle is 10cm wider that it is tall, the area is 28cm squared. find the height and base 1 solutions
Answer 195889 by drk(1908) on 2010-02-07 13:31:42 (Show Source):
You can put this solution on YOUR website!Let the height = h.
base = h + 10
area = 28
---
The area of a triangle has the formula

---
from the given information, we get

multiply both sides by 2 to get

distribute to get

set = 0 to get

factor to get

solving we get
h = -14
and
h = 4
we can't use the -14, so our only answer is
h = 4 cm
|
Polynomials-and-rational-expressions/266642: 18x^3-36x^2-38x-4 / 6x+4 1 solutions
Answer 195888 by drk(1908) on 2010-02-07 13:28:09 (Show Source):
You can put this solution on YOUR website!We can solve this by polynomial or synthetic division. Synthetic is faster. First, set 6x + 4 = 0 and solve for x as x = -2/3. Now divide as
(-2/3) // . . . . . . . . 18 . . . . . . -36. . . . . . -38 . . . . . . . -4
. . . . . . . . . . . . . . . . . . . . . . . . -12 . . . . . . 32 . . . . . . . . 4
. . . . . . . . . . . . . . . .18. . . . . . . -48. . . . . . .-6. . . . . . . . .0
---
we know one root is x = (-2/3)
we have
18x^2 - 48x - 6 = 0
divide by 6 to get
3x^2 - 8x - 1 = 0
using the quadratic, we get
x ~ 2.786
and
x ~ -0.1196
so, our 3 roots are
{-2/3, -.1196, and 2.786}
|
Mixture_Word_Problems/266638: how much water must be evaporated from 32 ounces of a 4% salt solution to make a 6% slat solution? 1 solutions
Answer 195885 by drk(1908) on 2010-02-07 13:15:03 (Show Source):
You can put this solution on YOUR website!this is a mixture problem. Here is a table based on the given information
solutions . . . . . . . % . . . . . . . . ounces . . . . . . . . . .%ounces
salt . . . . . . . . . . .4 . . . . . . . . .32 . . . . . . . . . . . . . . .128
water . . . . . . . . .0 . . . . . . . . . x . . . . . . . . . . . . . . . .0
mixture. . . . . . . 6 . . . . . . . . . x + 12. . . . . . . . . . . . 6x + 72
looking at the third column, we have

subtract 72 to get

dividing, we get
|
Linear-systems/266590: please help me solve for x and y
it takes bob the boy scout 10 hours to paddle upstream {against the current} a distance 15 miles. when he turns around he finds it only takes him 5 hour to paddle 22.5 miles with the current.how fast is bob's boat going in stilll water and what is the speed of the curent of the river?
please solve this problem right now!!!! thank you 1 solutions
Answer 195882 by drk(1908) on 2010-02-07 13:06:36 (Show Source):
You can put this solution on YOUR website!This is a RTD problem. Here is a table based on given information
paddle . . . . . . . . .rate . . . . . . . . . time . . . . . . . . . distance
up stream . . . . . .r - c . . . . . . . . . . .10 . . . . . . . . . . 10r - 10c =15
down stream . . . .r + c . . . . . . . . . . .5 . . . . . . . . . . .5r + 5c = 22.5
totals . . . . . . . . .
Looking at column 3 we get
(i) 10r - 10c = 15
(ii) 5r + 5c = 22.5
multiply (ii) by 2 to get
(iii) 10r + 10c = 45
add (i) and (iii) to get
(iv) 15r = 60
divide to get
(v) r = 4
This means that the current is
c = 2.5
|
Trigonometry-basics/266599: show that f(x)=(x-2)/(x+3) is invertible by finding its inverse.
(a) what is the domain of f(x)? the range of f-1(x)?
(b) what is the domain of f-(x)? the range of f(x)? 1 solutions
Answer 195872 by drk(1908) on 2010-02-07 11:44:32 (Show Source):
You can put this solution on YOUR website!Here is the original equation
(i) 
to find the inverse switch the x and y parts.
(ii) 
cross multiply to get
(iii) 
add 2 and then subtract xy to get
(iv) 
factor out the y to get
(v) 
divide by 1-x to get
(vi) 
this is the inverse
----
a). domain of f(x) is all reals except x = -3
The range of f^(-1)(x) is all reals except y = -3
b). The range of f(x) is all reals except y = 1
the domain of f^(-1)(x) is all reals except x = 1
|
Complex_Numbers/266600: how to solve with Given that (x+iy)/(2-i) , find x and y. 1 solutions
Answer 195871 by drk(1908) on 2010-02-07 11:38:41 (Show Source):
You can put this solution on YOUR website!we are given
(i) 
step 1 - multiply by the conjugate of (2-i) which is (2+i) to get
(ii) 
and simplified, we get
(iii) 
we then separate our real and imaginary parts to get
(iv)  + 
---
at this point there is no equal sign, so we can't solve for x and y, just rewrite using x and y in the real and imaginary parts.
|
Circles/266569: if a trampoline has a radius of 6.5 feet how much fencing is needed to go around the circumference 1 solutions
Answer 195867 by drk(1908) on 2010-02-07 10:31:36 (Show Source):
|
Equations/266557: Solve for the literal equation of X.
13(x+2g) - 3(4x+5g) = 0 1 solutions
Answer 195866 by drk(1908) on 2010-02-07 10:28:26 (Show Source):
You can put this solution on YOUR website!here is the original equation
(i) 
step 1 - distribute the 13 and the -3 to get
(ii) 
step 2- combine like terms to get
(iii) 
step 3 - solve for x to get
(iv)
|
Distributive-associative-commutative-properties/266564: when you look at a commutative and associative properties in algbra what is the difference between the two 1 solutions
Answer 195864 by drk(1908) on 2010-02-07 10:25:56 (Show Source):
You can put this solution on YOUR website!Commutative property is expressed as
a + b = b+ a
OR
a x b = b x a
The idea is that we are reversing our information.
----
Associative property is expressed as
(a + b) + c = a + (b + c)
OR
(a x b) x c = a x (b x c)
The order is the same, only parenthesis have shifted.
-----
that is the main difference.
|
Circles/266562: an ice cream cone has a radius of 2cm and a height of 7cm,what is the volume? 1 solutions
Answer 195861 by drk(1908) on 2010-02-07 10:22:17 (Show Source):
You can put this solution on YOUR website!The volume of a cone is
(i) 
where B = area of base (circle) and h = height.
from (i) we could say
(ii) 
Now from above, we get
(iii) 
or
(iv)
|
Graphs/266560: Solve by the substitution method
6m+n=23
m-6n=10
the solution is 1 solutions
Answer 195858 by drk(1908) on 2010-02-07 10:19:14 (Show Source):
You can put this solution on YOUR website!here is the original system:
(i) 
(ii) 
since we must use substitution, we can solve (i) for n and get
(iii) 
substitute (iii) into (ii) to get
(iv) 
distribute and simplify to get
(v) 
combine like terms to get
(vi) 
add 138 to get
(vii) 
divide by 37 to get
(viii) 
now,

So, we get
(4,-1)
|
|