问几道高中数学题目

第一题：
(2x-7)(2x+5)(x^2-9)-91
=(2x-7)(x+3)(2x+5)(x-3)-91
=(2x^2-x-21)(2x^2-x-15)-91
=(2x^2-x)^2-36(2x^2-x)+315-91
=(2x^2-x)^2-36(2x^2-x)+224
=(2x^2-x-8)(2x^2-x-28)
=(2x+7)(x-4)(2x^2-x-8)

第二题
(a+b-2ab)(a+b-2)+(1-ab)(1-ab)
=[(a+b)-2ab][(a+b)-2]+(1-ab)(1-ab)
=(a+b)^2-2(ab+1)(a+b)+4ab+(1-ab)^2
=(a+b)^2-2(ab+1)(a+b)+[4ab+(1-ab)^2]
=(a+b)^2-2(ab+1)(a+b)+(1+ab)^2
=[(a+b)-(ab+1)]^2
=[(a-1)(1-b)]^2
=(a-1)^2*(b-1)^2

第三题
x^4+y^4+(x+y)^4
=(x^2+y^2)^2-2x^2y^2+(x+y)^4
=[(x+y)^2-2xy]^2-2x^2y^2+(x+y)^4
=[(x+y)^2]^2-4xy(x+y)^2+4x^2y^2-2x^2y^2+(x+y)^4
=2(x+y)^4-4xy(x+y)^2+2x^2y^2
=2[(x+y)^4-2xy(x+y)^2+(xy)^2]
=2[(x+y)^2-xy]^2
=2(x^2+xy+y^2)^2.

第一题：
(2x-7)(2x+5)(x^2-9)-91
=(2x-7)(x+3)(2x+5)(x-3)-91
=(2x^2-x-21)(2x^2-x-15)-91
=(2x^2-x)^2-36(2x^2-x)+315-91
=(2x^2-x)^2-36(2x^2-x)+224
=(2x^2-x-8)(2x^2-x-28)