=Sin(?/14) Sin(3?/14) Sin(5?/14) Sin(7?/14) Sin(9?/14) Sin(11?/14) Sin(13?/14)

=Sin(?/14) Sin(3?/14) Sin(5?/14) Sin(?/2)sin(?-5?/14) sin(?- 3?/14)sin(?- ?/14)

=[ Sin(?/14) Sin(3?/14) Sin(5?/14)]^2

=[cos(?/2- ?/14)  cos(?/2-3?/14)  cos(?/2-5?/14)]^2

=[cos(3?/7) cos(2?/7) cos(?/7)]^2

= [cos(?/7) cos(2?/7) cos(3?/7)]^2

Multiplying and dividing by 2sin(?/7) we get

=[1/2sin(?/7)* (2sin(?/7) cos(?/7))* cos(2?/7) cos(3?/7)]^2

=[1/4sin(?/7)* (2sin(2?/7) cos(2?/7))* cos(4?/7)]^2

We can write cos(3?/7)=cos(?-4?/7)

                                         =cos(4?/7)

=[1/8sin(?/7)* (2sin(4?/7) cos(4?/7))]^2

=[ 1/8sin(?/7)* sin(8?/7)]^2

We can write sin(8?/7)=sin(?+?/7)

                                          = -sin (?/7)

=[1/-8]^2

=1/64            ( answer)