因式分解（要过程）急！！！！

显示全部楼层 · 2010-5-9 23:37:52

（1）x2-xy-30y2（2）x5-x3y-12xy4 (3)x3+3x2+3x+9
打不出来平方，数字在后面的都是平方

千问 · 2010-5-9 23:37:52

x^2-xy-30y^2=(x-6y)(x+5y)x^5-x^3y^2-12xy^4=x(x^4-x^2y^2-12y^4)=x(x^2-4y^2)(x^2+3y^2)=x(x-2y)(x+2y)(x^2+3y^2)x^3+3x^2+3x+9=x^2(x+3)+3(x+3)=(x+3)(x^2+3)

千问 · 2010-5-9 23:37:52

x^2-xy-30y^2=x^2+(5-6)xy+5×(-6)y^2=(x-6y)(x+5y) x^5-x^3y^2-12xy^4=x(x^4-x^2y^2-12y^4)=x[(x^2)^2-x^2y^2-12(y^2)^2]=x(x^2+3y^2)(x^2-4y^2)=x(x+2y)(x-2y)(x^2+3y^2)x