Iím not very good with the calculus of functions of two variables so I need someone to check my working below.
Prove that if x, y, z are the interior angles of a triangle, then .
I decided to use calculus to prove the result, so I defined a function of two variables
Since , we must have .
Hence f(x,y) has a maximum at , which is .
for all the angles x, y, z of a triangle. Is my working all okay?