因式分解：（1）3x^2+7x+2 (2)5x^2+13x-6=0 (3)6x^2+13x-15=0

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