definite integrals - Evaluating $\int_0^{2\pi} \sqrt{1+\cos^2(x)}\ dx$ - Mathema
I want to evaluate this integral $$\int_0^{2\pi} \sqrt{1+\cos^2(x)}\ dx$$ But I cannot find a useful substitution/strategy. Could you please give me a hint? I was thinking proving that ......