Question

Спростіть вираз $frac{sin9 alpha }{sin3 alpha } - frac{cos9 alpha }{cos3 alpha }$ , якщо $alpha neq frac{ pi n}{6}$

Answer 1

(sin9acos3a-cos9asin3a)/sin3acos9a=sin(9a-3a)/sin3acos9a=sin6a/sin3acos9a=
=2sin3acos3a/sin3acos9a=cos3a/cos9a