SOLUTION: What 2#'s multiplied equals -9 but added also equals -10?

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Question 1029733: What 2#'s multiplied equals -9 but added also equals -10?
Answer by fractalier(6550) About Me  (Show Source):
You can put this solution on YOUR website!
Let's call the numbers x and y. Then we can write
xy = -9 and x + y = -10
Solve the second one for y and substitute into the first one...we get
y = -x - 10
x(-x - 10) = -9
-x^2 - 10x = -9
x^2 + 10x = 9
x^2 + 10x - 9 = 0
This cannot be factored so we must solve using the quadratic formula...
x+=+%28-10+%2B+sqrt%28100+%2B+36%29%29%2F2
and
x+=+%28-10+-+sqrt%28100+%2B+36%29%29%2F2
Simplify and then find y...
I suspect there is a mistake in the problem...