№ 589
а) (x – 3)(x2 + 3x + 9) + 3x = x3x3 – 27 + 3x – x3 = 03x = 27x = 9;
б) (z – 4)(16 + 4z + z2) = z(z2 – 4)z3 – 64 = z3 – 4z4z = 64z = 64 : 4z = 16.
вправи поруч
