a²-b²+4a-4b=（a+2)²-(b+2)²=(a-b)(a+b+4)4x²-9y²-24yz-16z² =4x²-(3y+4z)²=(2x-3y-4z)(2x+3y+4z)x³-x²-x+1=（x-1）²（x+1)xy-1+x-y=(x-1)(y+1)m²...