Решите : 1.(2а-1)^2 2.(x+3y)^2 3.(7-x)*(7+x) 4.81-a^2 5.5x^2-5y^2 6.a^3+1/8у^3 7.3x^2-6xy+3y^2

1.(2а-1)^2 = 2a^2 - 4a + 1
2.(x+3y)^2 = x^2 + 6y + 9y^2
3.(7-x)*(7+x) = 49 - x^2
4.81-a^2 = (9-a)(9+a)
5.5x^2-5y^2 = 5(x-y)(x+y)
6.a^3+1/8у^3 =
7.3x^2-6xy+3y^2  = 3(x-y)^2