数学题(a分之b+c分之d)乘(b分之c+d分之a)

（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+_+