1、9x²=1 ====>>> (x)²=1/9 ===>>> x=±1/3
2、x²=4 ===>>> x±2
3、25x²=36 ==>> (x)²=36/25 ==>>> x=±6/5
4、(x＋6)²=9 ===>>> x＋6=±3 ==>>> x=－6±3 ==>>> x=－9或x=－3