Question

Срочно, пожалуйста, помогите!

Answer 1

Формулы:

$sinalpha +sinbeta =2sindfrac{alpha+beta }{2} cosdfrac{alpha-beta }{2} \cosalpha +cosbeta =2cosdfrac{alpha+beta }{2} cosdfrac{alpha-beta }{2}$

$dfrac{cos4alpha+cos2alpha}{sin4alpha+sin2alpha}=dfrac{2cosfrac{4alpha+2alpha}{2}cosfrac{4alpha-2alpha}{2}}{2sinfrac{4alpha+2alpha}{2}cosfrac{4alpha-2alpha}{2}}=dfrac{2cos3alphacosalpha}{2sin3alphacosalpha}=dfrac{cos3alpha}{sin3alpha}=mathrm{ctg}3alpha$