令a=x²-2x则a+7/a=8两边乘aa²-8a+7=0(a-1)(a-7)=0a=1,a=7x²-2x=1x²-2x-1=0x=1±√2x²-2x=7x²-2x-7=0x=1±2√2所以x=1-√2,x=1+√2,x=1-2√2,x=1+2√2