Question

cos 5pi/12-cos pi/12

Answer 1

$cos frac{5 pi }{12} -cos frac{ pi }{12} =-2sin frac{frac{5 pi }{12}+frac{ pi }{12}}{2} *sin frac{frac{5 pi }{12}-frac{ pi }{12}}{2} =-2sin{ frac{ pi }{4} }*sin frac{ pi }{6}=$$=-2* frac{ sqrt{2} }{2} * frac{1}{2} =- frac{ sqrt{2} }{2}$