十字相乘法分解因式x^2-7x+6; x^2+13+36; x^2+xy-6y^2; (x^2+x)^2-8(x^2+x)+12

x^2-7x+6;=(x-1)(x-6)x^2+13+36应该是x^2+13x+36吧下面是按x^2+13x+36来做的：x^2+13x+36=(x+4)(x+9)x^2+xy-6y^2=(x+3y)(x-2y)(x^2+x)^2-8(x^2+x)+12=(x^2+x-2)(x^2+x-6)=(x+2)(x-1)(x+3)(x-2)