（b/a+d/c）*(b/c+d/a)=b/a*b/c+b/a*d/a+d/c*b/c+d/c*d/a=c/a+b/d+b/d+c/a然后我求不出来了不过打的我要晕了+_+
d/(b+c)/a*a/(c+d)/b=d/[(b+c)/a]*[a/(c+d)]/b=d/[(b+c)/a]*{1/[(b+c)/a]}/b=(d*1)/b=d/b
求什么着呢
