(c²-a²-b²)²-4a²b²
=(c²-a²-b²)²-(2ab)²
=(c²-a²-b²＋2ab)(c²-a²-b²－2ab)
=[c²－(a²－2ab＋b²)][c²－(a²＋2ab＋b²)]
=[c²－(a－b)²][c²－(a＋b)²]
=(c＋a－b)(c－a＋b)(c＋a＋b)(c－a－b)
(c²-a²-b²)²-4a²b²
=(c²-a²-b²)²-(2ab)²
=(c²-a²-b²＋2ab)(c²-a²-b²－2ab)
=[c²－(a²－2ab＋b²)][c²－(a²＋2ab＋b²)]
=[c²－(a－b)²][c²－(a＋b)²]
=(c＋a－b)(c－a＋b)(c＋a＋b)(c－a－b)