Try yourself . Then look the solution:

The only way to achieve is using the first formula, , but we can only use it when is true, so we're going for that.

We know that (line 2) and also (line 3), so we deduce . Since is now true and also , is too. Until now it's similar to the previous exercise.

Finally, we have , and know that , so we finish by saying .

Daniel Clemente Laboreo 2005-05-17