The first part of the question asks you to show that for natural numbers x and y if ^x/_y > 1 then

x y > (x+1) (y+1) > 1.

Here's a hint for this: try starting with x > y, which you are given, and adding xy to both sides of the inequality.

For the next part of the question you are given a product P and the hint to consider P² and clearly the first part of the question should come in useful. Look out for a 'magic concertina' effect!!

If you can prove the second inequality then you will have shown that P gets bigger and bigger without limit as you put more terms into the product which proves that the product diverges, hence the title of the question!

For the last bit of the question, taking k=100 and repeating the last trick leads to the disappointing conclusion that Q² > 101, this estimate is not good enough.

Go back to the drawing board and do some neat estimating of Q² calculating the product of the first few terms exactly and using the concertina method on the rest. This will quickly give you the result. This is a good illustration of what mathematicians do all the time with inequalities. They go on sharpening them to get better and better estimates until they get close enough for their purposes.