(x+2)² => (a+b)² = a² + 2ab + b²
(x+2)² = x² + 2 × 2 × x + 2²
= x² + 4x + 4
(x-2)² => (a-b)²= a² - 2ab + b²
(x-2)² = x² - 2 × 2 × x + 2²
= x² - 4x + 4
(x+2)² - ( x-2)² =
( x² + 4x + 4 ) - (x² - 4x + 4 )
x² + 4x + 4 - x² + 4x - 4 ( se simplifica termenii asemenea ( x² ; - x² ; -4 ; 4 )
= 8x