x^2 + 6x - 40 = 0
(x + 10)(x - 4)= 0
x = -10 and x = 4

Llama11

x² + 6x = 40
x² + 6x - 40 = 0
Think of two numbers that multiply up to -40 and add up to give +6
The numbers are +10 and -4
Check: 10*-4 = -40. +10 + -4 = +6.
The +6 in the expression of the equation is replaced with 10 -6.
x² + 6x - 40 = 0
x² + 10x -4x - 40 = 0
x(x + 10) -4(x + 10) = 0
(x +10)(x - 4) = 0
x + 10 = 0 or x - 4 =0
x = 0 -10 or x = 0 +4
x = -10 or 4