Question

cos(п-a) - cos(-a),a=п/4

Answer 1

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