a(a+b)+b(a-b) = a^2 + ab + ab - b^2 = a^2 + 2ab - b^2
5a(6a+3b) - 6a(5b-2a) = 30a^2 + 15ab - 30ab + 12a^2 = 42a^2 - 15ab
a(a+b)+b(a-b) = a^2 + ab + ab - b^2 = a^2 + 2ab - b^2
5a(6a+3b) - 6a(5b-2a) = 30a^2 + 15ab - 30ab + 12a^2 = 42a^2 - 15ab