عمل ما يلي

$3x + 21 = 3x + 3 \times 7 = 3(x + 7)$

$4x - x^2 = x(4 - x)$

$-5x + 20 = -5x + 5 \times 4 = 5(-x + 4)$

$5x^2 - 8x = x(5x - 8)$

$(x - 1)(2x + 3) - (x - 1)(2 - x) = (x - 1)[(2x + 3) - (2 - x)] =$ $(x - 1)(2x + 3 - 2 + x) = (x - 1)(3x + 1)$

$(2x + 1)^2 + (2x + 1)(x + 3) = (2x + 1)[(2x + 1) + (x + 3)] =$ $(2x + 1)(2x + 1 + x + 3) = (2x + 1)(3x + 4)$

$(5x - 2)(2x + 7) - (5x - 2) = (5x - 2)[(2x + 7) - 1] =$ $(5x - 2)(2x + 6) = 2(5x - 2)(x + 3)$