(p的四次方+q的四次方)²-4p的四次方q的四次方
=p^8+2p^4q^4+q^8-4p^4q^4
=p^8-2p^4q^4+q^8
=(p^4-q^4)²
=【(p²-q²)(p²+q²)】²
=(p-a)²(p+q)²(p²+q²)²