Ответ:

х²+3х-7х-21-20х+8х²=9х²-24х-21

3z²-9z+z-3-10z²-15z+2z+3=-7z²-21z=-7z(z+3)

Объяснение:

1) (х + 3)(х - 7) - 4х(5 - 2х)

(х + 3)(х - 7)  = х² + 3х - 7x - 21 = х² - 4x - 21

4x(5 - 2x) = 20x - 8x²

(х + 3)(х - 7) - 4х(5 - 2х) = х² - 4x - 21 - 20x + 8x² = 9x² - 24x - 21

2) (z - 3)(3z + 1) - (2z + 3)(5z - 1)

(z - 3)(3z + 1) = 3z² - 9z + z - 3 = 3z² - 8z - 3

(2z + 3)(5z - 1) = 10z² + 15z - 2z - 3 = 10z² + 13z - 3

(z - 3)(3z + 1) - (2z + 3)(5z - 1) = 3z² - 8z - 3 - 10z² - 13z + 3 = -7z² - 21z = -7z(z + 3)