let each of those equal to k. Then

, , 











So 



Edwin

    In mathematics, a  lemma (a "helping theorem") is a proved proposition which is used as a stepping stone 
    to a larger result rather than as a statement of interest by itself. 

Lemma 1.  

    If  =  then  =  = .


        Proof. Let  =  = k. Then

               a = b*k,  c = d*k  and   =  =  = k =  = .

        The lemma is proved.



Lemma 2. 

    If  =  =   then   =  = .


       The proof is obvious.



Major statement.   = .


    Proof. It follows IMMEDIATELY Lemma 1  and  Lemma 2.