Question

cos(п-a) - cos(-a),a=п/4

Answer 1

$cos( pi-frac{pi}{4})-cos(-frac{pi}{4} )=-cos( frac{ pi }{4} )-cos( frac{ pi }{4} )=-2cos( frac{ pi }{4} )$
$-2* frac{ sqrt{2} }{2} =- sqrt{2}$