What times what equals 18 but when added equals negative 7?

Answer 1

25

Answer 2

Turn the question into equations form. The first "What" is x, the second "what" is y, and we have:

1) x * y = 18

2) x + y = -7

This is a system of linear equations. There are several ways to solve this, one of the more simpler ways, substitution, goes as follows:

Solve for x in equation 1

x = 18/y

Substitute x into equation 2

(18/y) + y = -7

Multiply y to both sides

18 + y2 = -7y

Move everything to one side

y2 + 7y + 18 = 0

This quadratic cannot be solved using factoring, and looking at the determinant (b2 - 4ac), we see that it has no solutions because it's negative.