SOLUTION: The sum of two numbers is 15.The sum of their squares is 9 more than 13 times the larger number.Find the numbers.

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Question 1092272: The sum of two numbers is 15.The sum of their squares is 9 more than 13 times the larger number.Find the numbers.
Found 2 solutions by richwmiller, greenestamps:
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
x+y=15
x^2+y^2=13*x+9

Answer by greenestamps(13203) About Me  (Show Source):
You can put this solution on YOUR website!

I nearly always find it easier to solve problems like this using a single variable instead of two. Given that the sum of the two numbers is 15, I would do

let x = large number
then (15-x) = smaller number

The sum of the squares of the two numbers is 9 more than 13 times the larger number:

x%5E2+%2B+%2815-x%29%5E2+=+13x%2B9
x%5E2+%2B+225+-+30x+%2B+x%5E2+=+13x%2B9
2x%5E2-43x%2B216+=+0
%282x-27%29%28x-8%29+=+0

This gives us two potential solutions:

(1) x = 8; 15-x = 7 OR
(2) x = 27/2; 15-x = 3/2

Since our solution method involved squaring expressions, we need to check to see which of the solutions actually satisfy the original problem.

For the first...

8%5E2%2B7%5E2+=+64%2B49+=+113 and
13%288%29%2B9+=+113

So that solution is valid.

For the second...

%2827%2F2%29%5E2+%2B+%283%2F2%29%5E2+=+729%2F4%2B9%2F4+=+738%2F4+=+369%2F2
13%2827%2F2%29%2B9+=+351%2F2%2B18%2F2+=+369%2F2

This solution is also valid.

So there are two solutions to the problem: 8 and 7; or 27/2 and 3/2.