Question 271070
x^2-x-72=0

Reverse Foil
A.What multiplied together will give you x^2? 
Answer x times x
B. What multiplied together will give you negative 72 and added will give you negative 1? 
Answer -9 times 8

Written as:
(x-9)(x+8)
And when you foil this you get your original problem of x^2-x-72

Now set both equal to zero

x-9=0
x=0+9
x=9

x+8=0
x=0-8
x=-8

Check both answers in original equation for correct answer.

9^2-9-72=0?
81-9-72=0?
72-72=0?Yes