原式=[(a-3c)+4b][(a-3c)-4b][a+(b-c)][a-(b-c)]
=[(a-3c)²-(4b)²][a²-(b-c)²]
=(a²-6ac+9c²-16b²)(a²-b²+2bc-c²)
=a^4-6a³c+9a²c²-16a²b²-a²b²+6ab²c-9b²c²+16b^4+2a²bc-12abc²+18bc³-32b³c-a²c²+6ac³-9c^4+16b²c²
=a^4+16b^4-9c^4-17a²b²+8a²c²+7b²c²-6a³c+18bc³-32b³c+6ac³+6ab²c+2a²bc-12abc²