（2a-1）²=02a-1=0a=1/2（2x-5）²=9 (2x-5)²-3²=0(2x-5+3)(2x-5-3)=0(2x-2)(2x-8)=0x=1 x=44x²-（x-1）²=0(2x-x+1)(2x+x-1)=0(x+1)(3x-1)=0x=-1 x=1/3