Question

cos(3pi/7)-cos(9pi/7) преобразовать в произведение
Даю 50 балов!!!

Answer 1

Ответ:     2sin( 6π/7 )*sin( 3π/7 ) .

Объяснение:

cos(3π/7) - cos(9π/7)= - 2sin[(3π/7+ 9π/7)/2]sin[(3π/7- 9π/7)/2] =

= + 2sin[ (12π/7 )/2 ] * sin[ 9π/7- 3π/7)/2 ] = 2sin( 6π/7 ) X

   X sin( 3π/7 ) .

 В - дь :     2sin( 6π/7 )*sin( 3π/7 ) .