（x²+x)²-26(x²+x)+120
=(x²+x-6)(x²+x-20)
=(x+3)(x-2)(x+5)(x-4)
ax+ay+bx+by-a-b
=a(x+y)+b(x+y)-(a+b)
=(a+b)(x+y)-(a+b)
=(a+b)(x+y-1)
x²(x²-y²)-72y⁴
=x⁴-x²y²-72y⁴
=(x²+8y²)(x²-9y²)
=(x²+8y²)(x+3y)(x-3y)