(1)(a的八次方-b的八次方)÷(a的四次方+b的四次方)÷(a²+b²)
=(a的四次方-b的四次方)÷(a²+b²)
=a²-b²
2)(3a的n+1次方+6a的n+2次方-9a的n次方)÷3a的n-1次方
=a²+2a的三次方-3a