x+x的倒数等于3,则x+x的负二次,等于
问题描述：
x+x的倒数等于3,则x+x的负二次,等于
答
x+1/x=3
(x+1/x)^2=3^2
x^2+2+1/x^2=9
x^2+1/x^2=7最后第二步后的过程x^2+2+1/x^2=9x^2+1/x^2=9-2x^2+1/x^2=7