51-x=12/x
x^2-51x+12=0
x^2-51x+(51/2)^2-(51/2)^2+12=0
(x-51/2)^2=2553/4
x-51/2=±√2553/2
x=(51±√2553)/2非常感谢，x^2-51x+(51/2)^2-(51/2)^2+12=0(x-51/2)^2=2553/4这一步怎么解的能再详细一点吗？这是配方法，即加一个51/2和减一个51/2结果不变，x^2-51x+(51/2)^2-(51/2)^2+12=0x^2-51x+(51/2)^2=(51/2)^2-12(x-51/2)^2=2553/4