Hello brumby_3When you used the Sine Rule to find , did you get ? If so, you need to remember that there are two possible values of that both have the same sine: and .

How do we tell which to choose? The answer is to find thesmallestangle of the triangle first (that's the one opposite the shortest side), because you know that one can't possibly be obtuse.

In this case that's , which turns out to be . Then add and together and subtract from to find .

Grandad