3x的平方-4x-7 因式分解
=(3x-7)(x+1)
a的2n次方+4a的n次方-12
=(a^n)²+4a^n-12
=(a^n+6)(a^n-2)
a的2n+1次方-9a的n+1次方+8a
=a(a^2n-9a^n+8)
=a(a^n-8)(a^n-1)