X^2+7x-8=0
D=b^2-4ac=81=9^2
x1=-8
x2=1
а) (9a - b)(81a² + 9ab + b²) = 729а³-b³.
б) (3a² + 1)(9a⁴ - 6a² + 1) = 27a⁶-18a⁴+3a²+9a⁴-6a²+1 = 27a⁶-9a⁴-3a²+1.
в) (3a + 1)(9a² - 6a + 1) = 27a³-18a²+3a+9a²-6a+1 = 27a³-9a²-3a+1.
г) <span>(3a² + 1)(3a - 1) = 9a</span>²-1.