Your book is wrong.

Now in the part where is says then it will equal 0. And you know that anything divided by 0 is undefined.

My answer:

Now we multiplyeverythingby giving us:

Cancel out like terms leaving:

And then divide everything by to get the answer:

Now we see the part where it says we know that it will be 0 because = 0. (I should have cancelled that out from the start...)

This leaves:

Can you carry on from there? Or am I wrong?