Question

What two numbers adds up to 7 but multiply to -8

Answer 1

Ans is 8 and -1

8 + (-1) = 7

and

8 * (-1) = -8

Answer 2

Let, the numbers = a, b

Then, a + b = 7
& a * b = -8

Substitute the value of a from Equation (1) into (2), 
(7-b) * b = -8
7b - b² = -8
b² - 7b - 8 = 0
b² + b - 8b - 8 = 0
b(b + 1) -8(b + 1) = 0
(b + 1)(b - 8) = 0
b = -1 OR 8

In short, Your Numbers would be: -1 & 8

Hope this helps!