（1）9(x-1)²-(x+2)²=0
[3(x-1)]²-(x+2)²=0
(3x-3+x+2)(3x-3-x-2)=0
(4x-1)(2x-5)=0
4x-1=0或2x-5=0
x1=1/4 x2=5/2
（2）2x²+2√2x+1=0
(√2x)²+2√2x+1=0
(√2x+1)²=0
√2x+1=0
x=-1/√2
x=-√2/2