sinA+2sin3A+sin5A/sin3A+2sin5A+sin7A
1个回答

sinA+sin5A=sin(3A-2A)+sin(3A+2A)

=2sin3Acos2A

同理有

sin3A+sin7A=2sin5Acos2A

所以

原式=(cos2A+1)sin3A/(cos2A+1)sin5A

=sin3A/sin5A