a)

x² - y² + x + y = (x - y)(x + y) + (x + y)

б)

(x+1)³-2(x+1)²+(x+1) = (x + 1) ((x + 1)² - 2(x + 1) + 1)=

= (x + 1)(x² + 2x + 1 - 2x - 2 + 1) = (x + 1)(x² - 1)

в)

5x- b+25x²-5bx = 5x - b(1 - 5x) + 5x(5x - 1) = 5x - b + 5x(5x - 1)