8x^2y^2+6xy-35
=(2x+5y)(4x-7y)
2（a+b)^2+（a+b）（a-b）-6（a-b)^2
=[2(a+b)-3(a-b)][(a+b)+2(a-b)]
=(2a+2b-3a+3b)(a+b+2a-2b)
=(5b-a)(3a-b)
y^2+2y-a^2+1
=y^2+2y+1-a^2
=(y+1)^2-a^2
=(y+1-a)(y+1+a)
7（x-1）^2+4（x-1）（y+2）-20（y+2）^2
=[(x-1)+2(y+2)][7(x-1)-10(y+2)]
=(x-1+2y+4)(7x-7-10y-20)
=(x+2y+3)(7x-10y-27)