The square of a negative number is fifteen more than twice the negative number. Find the number.
If n is the number then we can write
n2 = 2n + 15
Rearrange:
n2 - 2n - 15 = 0
This factorises as
(n - 5)(n + 3) = 0
so the the negative value of n that makes this true is n = -3
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