（2x+Y-z+5）（2x-y+z+5）=[(2x+5)+(y-z)][(2x+5)-(y-z)]=(2x+5)²－(y-z)²=4x²+20x+25-(y²-2yz+z²)=4x²+20x+25-y²+2yz-z²（a+3b+2c）（a-3b+6c）=a(a-3b+6c)+3b(a-3b+6c)+2...