14xy-28ay = 14y(x-2a)
20a^5b^3-15b^4 = 5 b^3 (4a^5 - 3b)
a(5-b)+7(5-b) = (a+7)(5-b)
a-b^2-b+a^2 = (a^2 + a) - (b^2+b) = a (a+1) - b(b+1) = (a-b) (a+b+1)
14xy-28ay = 14y(x-2a)
20a^5b^3-15b^4 = 5 b^3 (4a^5 - 3b)
a(5-b)+7(5-b) = (a+7)(5-b)
a-b^2-b+a^2 = (a^2 + a) - (b^2+b) = a (a+1) - b(b+1) = (a-b) (a+b+1)