Question

Sin4a+sin5a+sin6a / cos4a+cos5a+cos6a

Answer 1

sin4a + sin5a + sin6a   = sin4a + sin6a  + sin5a ,  2sin(5a)*cosa + sin5a = sin5a(2cosa+1)

cos4a + cos5a + cos6a =  cos4a + cos6a + cos5a , 2cos5a*cosa + cos5a  = cos5a(2cosa+1)

sin5a(2cosa+1)/cos5a(2cosa+1) = sin5a/cos5a = tg5a