2 numbers can be added to equal 7 and multiplied to equal -120?

Answer 1

Assume that the two numbers are represented by 'x' and 'y':

x+y=7 and xy= -120

As x+y=7, re-arrange the formula so that x=7-y

Now substitute for x: (7-y)y = -120

7y-y2= -120

7y-y2+120 = 0

y2_7y-120 = 0

(y-15)(y+8) = 0

Therefore y = 15 or -8, and so putting back into the original equation, when y=15,

x = -8, and when y= -8, x = 15