中二數學問題 (20分)!!!!急急急急急!!!!!!!!!

1)
72(x+y)^2 - 8(x-y)^2
=8[9(x+y)^2-(x-y)^2]
=8[(3x+3y)^2-(x-y)^2]
=8[(3x+3y)+(x-y)][(3x+3y)-(x-y)]
=8(3x+3y+x-y)(3x+3y-x+y)
=8(4x+2y)(2x+4y)
=32(2x+y)(y+2x)

2)
75(s-3t)^2 - 27(2s-5t)^2
=3[25(s-3t)^2-9(2s-5t)^2]
=3[(5s-15t)^2-(6s-15t)^2]
=3[(5s-15t)+(6s-15t)][(5s-15t)-(6s-15t)]
=3[5s-15t+6s-15t][5s-15t-6s+15t]
=3[11s-30t][-s]
=3s(30t-11s)

3)
a^2 - b^2 + bc - ac
=(a+b)(a-b)+c(b-a)
=-(a+b)(a-b)-c(a-b)
=(a-b)(a+b-c)

4)
12v - 12v^2 - 6u + 3u^2
= 3u^2 - 12v^2 - 6u + 12v
= 3[(u^2 - 4v^2) - 2(u - 2v)]
= 3[(u+2v)(u-2v) - 2(u-2v)]
= 3(u-2v)[(u+2v)-2]
= 3(u-2v)(u+2v-2)

一個字~~~(勁)

1)
72(x+y)^2 - 8(x-y)^2
= 72(x^2 + 2xy + y^2) - 8(x^2 - 2xy + y^2)
= 72x^2 + 144xy + 72y^2 - 8x^2 + 16xy - 8y^2
= 64x^2 + 160xy + 64y^2
= 32(2x^2 + 5xy + 2y^2)
= 32(2x + y)(x + 2y)

2)
75(s-3t)^2 - 27(2s-5t)^2
= 75(s^2 - 6st + 9t^2) - 27(4s^2 - 20st + 25t^2)
= 75s^2 - 450st + 675t^2 - 108s^2 + 540st - 675t^2
= -33s^2 + 90st
= -3s(11s + 30t)

3)
a^2 - b^2 + bc - ac
= (a+b)(a-b) + c(b-a)
= (a+b)(a-b) - c(a-b)
= (a-b)(a+b-c)

4)
12v - 12v^2 - 6u + 3u^2
= 3u^2 - 12v^2 - 6u + 12v
= 3(u^2 - 4v^2) - 6(u - 2v)
= 3(u+2v)(u-2v) - 6(u-2v)
= (u-2v)[ 3(u+2v) - 6 ]
= (u-2v)(3u+6v-6)
= 3(u-2v)(u+2v-2)