Youreallyneed to work on your notation.

I would translate what you wrote into something more meaningful, but there are too many conceptual errors in there to make it worth the effort.

We know that

and .

Thus

.

This means that q is in either quadrant II or quadrant III. Given that , we can reduce this to q being in quadrant II.

So, to find , just use . The value of will be positive since q is in QII.

Now the rest is easy:

-Dan