3x²-4xy-2y²
=5x²-2(x²+2xy+y²)
=5x²-2(x+y)²
=(√5x)²-[√2(x+y)]²
=[√5x+√2(x+y)][√5x-√2(x+y)]
=[(√5+√2)x+√2y][(√5-√2)x-√2y]
2a²-3ab-b²
=2[a²-2×a×3b/4+(3b/4)²-17b²/16]
=2[(a-3b/4)²-(√17b/4)²]
=2[a-(3-√17)b/4][a-(3+√17)b/4]