If (1+sina) (1+sinb) (1+sinc) = (1-sina) (1-sinb) (1-sinc) = k then value of k=?

a. (cosacosbcosc)

b. (sinasinbsinc)

c. (3sinasinbsinc),

k = (1+sina) (1+sinb) (1+sinc) = (1-sina) (1-sinb) (1-sinc) Multiply both entities, k x k = (1+sina) (1+sinb) (1+sinc) x (1-sina) (1-sinb) (1-sinc) That gives k^2 = (1 - sin^2a) (1 - sin^2b) (1 - sin^2c) k^2 = (cos^2a) x (cos^2b) x (cos^2c) k = sqrt ((cos^2a) x (cos^2b) x (cos^2c)) k = cosacosbcosc option a is correct.