Other trigonometric proofs of Pythagoras theorem

Abstract

Only very recently a trigonometric proof of the Pythagoras theorem was given by Zimba \cite{1}, many authors thought this was not possible. In this note we give other trigonometric proofs of Pythagoras theorem by establishing, geometrically, the half-angle formula $\cos \theta =1-2{\sin }^2\frac{\theta }{2}$.