# One angle of triangle

• January 25th 2010, 06:22 AM
Stuck Man
One angle of triangle
I'm not sure what formula is needed to answer the attached question. Maybe the half angle formulae?
• January 25th 2010, 06:35 AM
Hello Stuck Man
Quote:

Originally Posted by Stuck Man
I'm not sure what formula is needed to answer the attached question. Maybe the half angle formulae?

$\sin A = \sin(\pi-A)$
$=\sin(B+C)$

$=\sin B\cos C + \cos B \sin C$
Can you see it OK from here?