Maths Question:
$\text{If }A,\text{ }B\,\text{and }C\text{ are angles of a triangle prove that }\cot (A+B)+\cot C=0$
Maths Solution:
$\begin{align} & A+B+C=\pi \\ & A+B=\pi -C \\ & \cot (A+B)=\cot (\pi -C) \\ & \cot (A+B)=-\cot C \\ & \cot (A+B)+\cot C=0 \\\end{align}$
University mathstopic: