(7x - 3)² - (5x - 8)(7x - 3)
= (7x - 3)[(7x - 3) - (5x - 8)]
= (7x - 3)(7x - 3 - 5x + 8)
= (7x - 3)(2x + 5)

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

6(x + 7)(3 - x) + 3(x + 7)(1 - x)
= 3(x + 7)*2*(3 - x) + 3(x + 7)(1 - x)
= 3(x + 7)[2(3 - x) + 1 - x]
= 3(x + 7)(6 - 2x + 1 - x)
= 3(x + 7)(-3x + 7) .

-7x(3x + 1) + 3x + 1
= -7x(3x + 1) + (3x + 1)*1
= (3x + 1)(-7x + 1) .

x - 5 - 4(x - 5)²
(x - 5)*1 - 4(x - 5)²
(x - 5)(1 - 4x + 20)
= (x - 4)(-4x + 21) .

28(x - 1) + 7x(x - 1)
(x - 1)(28 + 7x)
(x - 1)(7*4 + 7x)
=(x - 1)*7*(4 + x) = 7(x - 1)(x + 4) .