x^2 - 3x +1 = 0同除以xx - 3 + 1/x = 0x + 1/x = 3(x+1/x)^2 = x^2 + (1/x)^2 + 2(x-1/x)^2 = x^2 + (1/x)^2 - 2 = (x+1/x)^2 - 4 = 9 - 4 = 5故原式 = 根号5
