integral-assertion reason

can u show how to get statement A?

Using the property \int_{a}^{b}{f(x)dx} = \int_{a}^{b}{f(a+b -x)dx}

we have

I = \int_{0}^{\pi}{\frac{dx}{1+5^{cosx}}} = \int_{0}^{\pi}{\frac{dx}{1+5^{-cosx}}} = \int_{0}^{\pi}{\frac{5^{cosx}dx}{1+5^{cosx}}}

so now 2I = \int_{0}^{\pi}{\frac{1+5^{cosx}}{1+5^{cosx}}}dx = \int_{0}^{\pi}{dx} = \pi

so I = π/2

oh i got till the last step but didnt wrote I instead of 2I.......thx.....