Question

cosa+cos3a/sin3a-sina=

Answer 1

$frac{cosa+cos3a}{sin3a-sina}= frac{2cos frac{3a+a}{2} *cos frac{3a-a}{2} }{2cos frac{3a+a}{2} *sin frac{3a-a}{2}}= frac{cos2a*cosa}{cos2a*sina} =ctga$