It is given that:

$\displaystyle

Sin7\theta = 7Sin{\theta} - 56Sin^3\theta + 112Sin^5\theta - 64Sin^7\theta

$

Hence, prove that the only real solution of the equation

$\displaystyle Sin 7 \theta = 7Sin\theta$

are given by

$\displaystyle

\theta = n\pi

$

Where n is an integer.

I am really stuck with this :(

Any help would be greatly appreciated.

Thankyou.