For non-negative integers $a$ and $b$, let $I(a,b)=\displaystyle\int_0^{\pi/2}\cos^a x\cos bx\,dx$.
Match each entry in List-I to the correct entry in List-II.
**List-I:** P) $I(0,5)$; Q) $I(1,4)$; R) $I(2,4)$; S) $I(3,2)$
**List-II:** 1) $\dfrac{1}{5}$; 2) $\dfrac{1}{5}I(2,1)$; 3) $\dfrac{1}{4}[I(1,3)-I(1,5)]$; 4) $\dfrac{1}{5}I(0,3)$; 5) $\dfrac{1}{3}I(2,1)$