Antwort
$\int_a^b f(x)\,dx = \int_a^b f(a + b - x)\,dx$. In particular, $\int_0^a f(x)\,dx = \int_0^a f(a - x)\,dx$.
Erklärung
Adding the original integral $I$ to the transformed integral often eliminates transcendental or trigonometric denominators.