Explanation
Let $$I = \int\limits_0^{100\pi } {\sqrt {1 - \cos 2x} dx} $$
$$I = \int\limits_0^{100\pi } {\sqrt {2{{\sin }^2}x} dx} $$
$$ = \int\limits_0^{100\pi } {\sqrt 2 \sin xdx} $$
$$ = - \sqrt 2 \left[ {\cos x} \right]_0^{100\pi }$$
$$ = - \sqrt 2 \left( {\cos 100\pi - \cos 0} \right)$$
$$ = - \sqrt 2 \left( {1 - 1} \right)$$
$$ = 0$$
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