SOLUTION: The sum of the squares of two consecutive integers is 9 greater than 8 times the smaller integer. Find the integers.

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Question 391464: The sum of the squares of two consecutive integers is 9 greater than 8 times the smaller integer. Find the integers.
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

two consecutive integers are n, n +1
n+%3C+n+%2B1
The sum of the squares of two consecutive integers is n%5E2+%2B%28+n+%2B1%29%5E2
n%5E2+%2B%28+n+%2B1%29%5E2+=+8n+%2B9
n%5E2+%2B+n%5E2+%2B2n+%2B1+=+8n+%2B9
2n%5E2++%2B2n+%2B1+=+8n+%2B9

2n%5E2++%2B2n++-8n+=+9+-+1
2n%5E2++-+6n+=+8
2n%5E2+%2F2+-+6n%2F2+=+8%2F2



n%5E2++-+3n+-+4=0........solve for n
Solved by pluggable solver: Quadratic Formula
Let's use the quadratic formula to solve for x:


Starting with the general quadratic


ax%5E2%2Bbx%2Bc=0


the general solution using the quadratic equation is:


x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29




So lets solve x%5E2-3%2Ax-4=0 ( notice a=1, b=-3, and c=-4)





x+=+%28--3+%2B-+sqrt%28+%28-3%29%5E2-4%2A1%2A-4+%29%29%2F%282%2A1%29 Plug in a=1, b=-3, and c=-4




x+=+%283+%2B-+sqrt%28+%28-3%29%5E2-4%2A1%2A-4+%29%29%2F%282%2A1%29 Negate -3 to get 3




x+=+%283+%2B-+sqrt%28+9-4%2A1%2A-4+%29%29%2F%282%2A1%29 Square -3 to get 9 (note: remember when you square -3, you must square the negative as well. This is because %28-3%29%5E2=-3%2A-3=9.)




x+=+%283+%2B-+sqrt%28+9%2B16+%29%29%2F%282%2A1%29 Multiply -4%2A-4%2A1 to get 16




x+=+%283+%2B-+sqrt%28+25+%29%29%2F%282%2A1%29 Combine like terms in the radicand (everything under the square root)




x+=+%283+%2B-+5%29%2F%282%2A1%29 Simplify the square root (note: If you need help with simplifying the square root, check out this solver)




x+=+%283+%2B-+5%29%2F2 Multiply 2 and 1 to get 2


So now the expression breaks down into two parts


x+=+%283+%2B+5%29%2F2 or x+=+%283+-+5%29%2F2


Lets look at the first part:


x=%283+%2B+5%29%2F2


x=8%2F2 Add the terms in the numerator

x=4 Divide


So one answer is

x=4




Now lets look at the second part:


x=%283+-+5%29%2F2


x=-2%2F2 Subtract the terms in the numerator

x=-1 Divide


So another answer is

x=-1


So our solutions are:

x=4 or x=-1




x=n
so, you have
n1=4 and
second integer n1+%2B1=+4%2B1=5
4 and 5
n2=+-1
second integer n2+%2B1=+-1%2B1=0
-1 and 0
check: 4 and 5
4%5E2+%2B%28+5%29%5E2+=+8%2A4+%2B9
16+%2B25+=+32+%2B9
41+=+41
other pair: -1 and 0
%28-1%29%5E2+%2B%28+0%29%5E2+=+8%2A%28-1%29+%2B9
1+%2B0+=+-8+%2B9
1+%2B0+=+1