What multiplies to 8 and adds to negative 15?

Answer 1

23

Answer 2

Let the number be 'm' & 'n'

Hence

mn = 8

m + n = -15

Hence

m = -n - 15

Substitute

(-n - 15) n = 8

Multiply out the brackets

-n^2 - 15n = 8

Equate to zero .

n^2 + 15n + 8 = 0

It is now in quadratic form, and does not factor. Hence use the Quadratic Eq'n.

n = {-15 +/-sqrt[(15^2 - 4(1)(8)]} / 2(1)

n = { -15 +/-sqrt[225 - 32]} / 2

n = {-15 +/-sqrt[193]}/2

n= {-15 +/-13.892... } /2

n = -28.892... /2 & -1.1075... /2

n = -14.446... & -0.55375 are the two answers.