Ответ:
1. a) 5x - 25y = 5(x-5y)
b) 2ab - ac = a(2b - c)
2. a) 3az + 6ac - 9ab = 3a(z + 2c - 3b)
b) x^3y - 4xy^2 = xy(x^2 - 4y)
3. ab + bc / ax + cx = b(a+c) / x(a+c) = b / x
4. 4c^2 - 4a / ab^3 - b^3c^2 = 4(c^2-a) / b^3(a-c^2) = 4/b^3, подставляем 4/2^3 = 4/8 = 1/2