1. 计算:
(1) $-3x^2(2x - 4y) + 2x(x^2 - xy)$.
(2) $(2x - y)(x + y) - (x - y)^2$.
(3) $(27x^3 + 18x^2 - 3x) ÷ (-3x)$.
(4) $(x + 2y)^2 + (x - 2y)(x + 2y) + x(x - 4y)$.
(5) $(a^2b - 4ab^2 + b) ÷ b - (a + b)(a - b)$.

(1)
$=-6x^3+12x^2y+2x^3-2x^2y$
$=-4x^3+10x^2y$.
(2)
$=2x^2+2xy-xy-y^2-(x^2-2xy+y^2)$
$=2x^2+xy-y^2-x^2+2xy-y^2$
$=x^2+3xy-2y^2$.
(3)
$=27x^3 ÷ (-3x) + 18x^2 ÷ (-3x) - 3x ÷ (-3x)$
$=-9x^2-6x+1$.
(4)
$=x^2+4xy+4y^2+x^2-4y^2+x^2-4xy=3x^2$.
(5)
$=a^2-4ab+1-(a^2-b^2)$
$=a^2-4ab+1-a^2+b^2$
$=-4ab+1+b^2$.

2. 先化简,再求值:
(1)$(x+y)(x-y)+(x+y)^2-(6x^2y+4xy^2)÷2y$,其中$x=-2,y=\frac{1}{3}$.
(2)$[(x-y)(x+2y)-(x+y)^2]÷y$,其中$(x-2)^2+|1+y|=0$.
(3)$(x+1)^2-(x+1)(2x-1)$,其中$x^2-x+1=0$.
(4)$(x-y)(y-x)-[-y^2+2x(x-y)]$,其中$x=\frac{1}{2},y=-2$.

(1)
$=x^2-y^2+x^2+2xy+y^2-3x^2-2xy$
$=-x^2$.
当 $x=-2,y=\frac{1}{3}$时，
原式$=-(-2)^2=-4$.
(2)
$=(x^2+xy-2y^2-x^2-2xy-y^2)÷y$
$=(-3y^2-xy)÷y$
$=-3y-x$.
∵ $(x-2)^2+|1+y|=0$,
∴ $x-2=0,1+y=0$.
解得 $x=2,y=-1$.
∴ 原式$=-3×(-1)-2=3-2=1$.
(3)
$=x^2+2x+1-(2x^2+x-1)$
$=x^2+2x+1-2x^2-x+1$
$=-x^2+x+2$.
∵ $x^2-x+1=0$,
∴ $x^2-x=-1$.
∴ 原式$=-x^2+x+2$
$=-(x^2-x)+2$
$=1+2=3$.
(4)
$=2xy-x^2-y^2-(-y^2+2x^2-2xy)$
$=2xy-x^2-y^2+y^2-2x^2+2xy$
$=-3x^2+4xy$.
当 $x=\frac{1}{2},y=-2$ 时，
原式$=-3×(\frac{1}{2})^2 +4×\frac{1}{2}×(-2) = -4\frac{3}{4}$.