• # question_answer 5) What is the value of $\left( co{{s}^{2}}\text{ }67{}^\circ -si{{n}^{2}}23{}^\circ \right)$?

 We have, $co{{s}^{2}}67{}^\circ -si{{n}^{2}}23{}^\circ$ $=co{{s}^{2}}67{}^\circ -co{{s}^{2}}\left( 90{}^\circ -23{}^\circ \right)$ [$\because$$sin\left( 90{}^\circ -\theta \right)=cos\theta$] $=co{{s}^{2}}67{}^\circ -co{{s}^{2}}67{}^\circ$ $=0$