（1）x^2-3x+2=0
(x-1)(x-2)=0
x=1 x=2
(2）3x^2+10x+3=0
(x+3)(3x+1)=0
x=-3 x=-1/3
(3）x(x-7)=0
x=0 x=7
(4)x^2-4=0
(x+2)(x-2)=0
x=2 x=-2
(5)(x-2)(x-1)=0
x=2 x=1
结题很辛苦,Thanks.