Question

It cotoA=2 Then find sin3A CosA = sin7A cosA​

Answer 1

Answer:

sinA sinB= 2 cosA cosB

now sinA sinB –cosA cosB= cosA cosB

thus cos (A+B)= cosA cosB

now in a triangle, A+B= \pi–C

thus cos(\pi–C) = cosA cosB

so cosA*cosB/cosC= – 1