第五题,快,
收起
原式 = 1/(x^2 + 1 + 1/x^2)x^2+1/x^2 = (x + 1/x)^2 - 2 = 3^2 - 2 = 71/(x^2 + 1 + 1/x^2) = 1/(7+1) = 1/8