①-12abc(3a+4b-2c)②(x-3y)(x-1/2y)③(x+2y)^2(x-2y)^2④(a-2b+c)(a+2b+c)在线的数学专家们帮帮我

①-12abc(3a+4b-2c)
=-36a²bc-48ab²c+24abc²
②(x-3y)(x-1/2y)
=x²-xy/2-3xy+3y²/2
=x²-7xy/2+3y²/2
③(x+2y)^2(x-2y)^2
=[(x+2y)(x-2y)]²
=(x²-4y²)²
=x的4次方-8x²y²+16y的4次方
④(a-2b+c)(a+2b+c)
=[(a+c)-2b][(a+c)+2b]
=(a+c)²-4b²
=a²+2ac+c²-4b²