Question

Solve this equation using an algebraic method: (x + 4)( x - 4) = 9

Answer 1

use FOIL method first to get rid of ()
x^2 - 4x + 4x -16 = 9
x^2 - 16 = 9
move the 16 over by addition
x^2 = 25
Then take the square root and get
x = 5

Answer 2

perform indicated operations on left side

x*x+4x+4x+4*4=9

x^2+4x+4x+16=9  combine like terms on left side

x^2+8x+16=9  subtract 9 from both sides

x^2+8x+7=0  factor

x^2+x+7x+7=0

x(x+1)+7(x+1)=0

(x+7)(x+1)=0

x=-1, -7