Well, I have a problem. These are some exercises from the Koshy's book about Number Theory...

The first is:

Verify that $\displaystyle $\tbinom{n}{r}=\frac{n}{r}\tbinom{n-1}{r-1}$$.

That is easy, I did this:

Then the next one was:

Show that:

I tried to prove it using Mathematical Induction, but I don't get to the result...

I'll show what I've done:

But I don't know how to get to where I wanna get...