ab/a+b=1/3 1/[1/b+1/a]=1/3 1/b+1/a=3
bc/b+c=1/4 1/[1/c+1/b]=1/4 1/c+1/b=4
ac/a+c=1/5 1/[1/c+1/a]=1/5 1/c+1/a=5
三个式子相加得 1/a+1/b+1/c=6
abc/ab+bc+ca=1/[1/a+1/b+1/c]=1/6
x/x^2-x+1=7 (x^2-x+1)/x=x+1/x-1=1/7
x+1/x=8/7 x^2+2+1/x^2=64/49 x^2+1/x^2= 题目你查一下原题
x^2/x^4+x^2+1=1/[x^2+1/x^2+1]