If `7 theta = (2n +1) pi, ` where `n = 0 , 1, 2, 3, 4,5, 6` then on the basis of above information, answer the following questions
The equation whose roots are `cos pi//7 , cos 3pi//7, cos 5pi//7` is

Options

A. `8x^(3) + 4x^(2) + 4x + 1 = 0`
B. `8x^(3) - 4x^(2) - 4x + 1 = 0`
C. `8x^(3) - 4x^(2) - 4x - 1 = 0`
D. `8x^(3) + 4x^(2) + 4x - 1 = 0`

Answer

B