What two numbers multiply together to equal -15 and add together to equal -7?

Answer 1

x + y = -7

xy = -15

y = -x - 7

x(-x - 7) = -15

-x^2 - 7x = -15 multiplying both sides by -1

x^2 + 7x = 15 complete the square;

(x^2 + 7x + 49/4) = 15 + 49/4

(x + 7/2)^2 = 109/4

(x + 7/2) = (plus & minus)square root of 109/4

1. x = -7/2 + (square root of 109)/2

2. x = -7/2 - (square root of 109)/2

y = -x - 7

y = -[-7/2 + (square root of 109)/2] - 7 = 7/2 - (square root of 109)/2 - 7

1. y = -7/2 - (square root of 109)/2 or

y = -x - 7

y = -[-7/2 - (square root of 109)/2] - 7 = 7/2 + (square root of 109)/2 - 7

2. y = -7/2 + (square root of 109)/2 Check it: