3x²+4xy-y²因式分解 3x²+4xy-y²=3(x²+4xy/3)-y²=3[(x+2y/3)²-4y²/9]-y²=3(x+2y/3)²-4y²/3-y²=[(√3)(x+2y/3)]²-[y√(7/3)]²=[(√3)(x+2y/3)...