Here is a question we had on an assignment a while back, the damn thing was only worth 2 marks yet it took the guy the whole lecture to explain the answer. dumb. But anyway, here's the question and the solution.

What I want to know is whether there is an easier way to do this. I don't understand the N(b) bit in the solution and frankly for a 2 mark question it was far too easy to get half/zero marks considering the guy is the most stringent marker I've ever encountered and the solution is fairly long.

Show that,

.

I thought it would just be a simple, let and go from there but apparently not...

Solution is in attachment.