（1）3x^2+7x+2 =3x^2+6x+x+2=3x(x+2)+(x+2)=(x+2)(3x+1)(2)5x^2+13x-6=0 5x^2-2x+15x-6=0x(5x-2)+3(5x-2)=0(5x-2)(x+3)=0x=2/5,x=-3(3)6x^2+13x-15=06x^2+18x-5x-15=06x(x+3)-5(x+3)=0(x+3)(6x-5)=0x=-3,x=5/6