SOLUTION: Find two negative numbers such that the square of their sum is 20 more than the square of their difference, and the difference of their squares is 24. I have an upcoming mathlet

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Question 10603: Find two negative numbers such that the square of their sum is 20 more than the square of their difference, and the difference of their squares is 24.
I have an upcoming mathletes compitition, and this problem has me stumpted.

Answer by longjonsilver(2297) About Me  (Show Source):
You can put this solution on YOUR website!
let 2 numbers be x and y.

%28x%2By%29%5E2+=+20+%2B+%28x-y%29%5E2 --eqn1
also, x%5E2+-+y%5E2+=+24 --eqn2

eqn1 becomes x%5E2+%2B+2xy+%2B+y%5E2+=+20+%2B+x%5E2+-+y%5E2
2xy+%2B+2y%5E2+=+20
xy+%2B+y%5E2+=+10
xy+=+10+-+y%5E2... now square both sides
so, %28xy%29%5E2+=+%2810+-+y%5E2%29%5E2
which is x%5E2y%5E2+=+100+-+20y%5E2+%2B+y%5E4

eqn2 becomes x%5E2+-+y%5E2+=+24
x%5E2+=+y%5E2+%2B+24

Sub this into eqn1, to give
%28y%5E2+%2B+24%29y%5E2+=+100+-+20y%5E2+%2B+y%5E4
y%5E4+%2B+24y%5E2+=+100+-+20y%5E2+%2B+y%5E4
44y%5E2+=+100
y%5E2+=+100%2F44
y%5E2+=+25%2F11
y+=+-sqrt%2825%2F11%29 ..just take the negative version, since the question asked for that.
y+=+-5%2Fsqrt%2811%29

now, x%5E2+=+y%5E2+%2B+24, so x%5E2+=+%2825%2F11%29+%2B+24
--> x^2 = 289/11
--> x+=+-sqrt%28289%2F11%29%29
--> x+=+-17%2Fsqrt%2811%29%29

check:
%28x%2By%29%5E2 is 44
%28x-y%29%5E2 is 13.09
so this is wrong!, since it should differ by 20.

and x%5E2+-+y%5E2 is 289/11 - 25/11 which is 24... correct.

so there might be something i am glaringly missing here...check my working: the method is correct!

jon.