x^2-5x+25/4-25/4-6=0(x-5/2)^2=49/4两边开平方得：x-5/2=±7/2x1=6 x2=-1 其实这题用十字相乘法比较容易：x^2-5x-6=0(x-6)(x+1)=0x-6=0 x+1=0x1=6 x2=-1
得(x+1)(x-6)=0所以x=-1或者x=6
x�0�5－5x-6=0 ﹙x-6﹚﹙x+1﹚＝0 x1=6 x2=-1
(x-6)(x+1)
