What would be the fastest way to do this question?
Is there a faster way than this:
First, Pythagoras Theorem gives
I then expanded it (?!) and used the quadratic formula (?!) and then took me a while to reject the "negative" answer. So
Finally, when the answer came out, it had a different form from the options (
), so I had to spend seconds to evaluate the options, esp D and E. Overall took rather long (>5 min).
Anyone has a faster method, that preferably produces an answer in the squared-form? Thanks a lot.