Question

When the square of a certain number is diminished by 9 times the number the result is 36?

Answer 1

x²-9x=36
minus 36 both sides
x²-9x-36=0
what 2 numbers multiply to -36 and add to -9
-12 and 3
(x-12)(x+3)=0
set to zero
x-12=0
x=12

x+3=0
x=-3



the number is either -3 or 12