Can someone please help me with the following problem and solution set:

I looked through my text and understand the properties reguarding phase difference in current and volatge for capicitors and inductors. I also understand impedance and how its calculated with regards to R L and C. My problem with this particular problem is the solution.

How can we use a triangle to solve this problem? I know in an inductor Current lags voltage by 90 degrees. But the solution above doesn not make sense to me, where does this triangle come from? Immediately I thought of applying KVL, can someone provide some more intuition please?

Thank you for your help.