x+1/x=4平方得:x²+2+1/x²=16移项得; x²+1/x²=14故(x-1/x)²=x²+1/x²-2=14-2=12
(x+1/x)²=x²+1/x²+2=16(x-1/x)²=x²+1/x²-2=12