3x^2-5x-2=0
十字相乘
(3x+1)(x-2)=0
(3x+1)=0 或 (x-2)=0
x=-1/3 或x=2配方法呢3x^2-5x-2=03(x^2-5x/3)-2=03[x^2-5x/3+(5/6)²]=2+(5/6)²×33(x-5/6)²=49/12(x-5/6)²=49/36=(7/6)²x-5/6=7/6或者x-5/6=-7/6x=7/6+5/6=2 或者x=5/6-7/6=-1/3有帮助请采纳 谢谢