[(-a)^4]^3 ÷ [a^2*(-a)^3]^2
=[ a^4]^3÷[a^2*(-a^3)]^2
=a^12 ÷ ( - a^5)^2
=a^12 ÷a^10 = a^2
(2) [(2x - y)(2x + y) + 2y(y - 6x) - (3x - y)^2]
= 4x^2 - y^2 + 4y^2 - 12xy - 9x^2 + 6xy - y^2
= (4x^2 - 9x^2) + (-12xy + 6xy ) + ( -y^2 + 4y^2 - y^2)
= - 5x^2 - 6xy + 2y^2
(3) 2x^2 - 8 x + 8 = 2(x^2 - 4x + 4) = 2(x - 2)^2
(4) (-a)^4 * (-a^2)^3 = a^4* (-a^6) = -a^10
(5) 因为：x + y = 3 xy = 1
所以 x^2 + y^2 = x^2 + 2xy + y^2 - 2xy
= ( x + y)^2 - 2xy
= 3^2 - 2×1
= 7
（6） x^3 - 4xy^2 = x(x^2 - 4y^2)
= x(x + 2y)(x - 2y)
(7) 2x^2y - 8xy + 8y =2y(x^2 - 4x + 4)
= 2y(x - 2)^2
(8) x^2 - 8x + 7 = (x - 7) (x - 1)
(9) x^2 + 7x -18 = ( x + 9)(x - 2)