$\mathrm {\int \cos ^{2} 3 x ~d x=}$ কত?

$\mathrm {\dfrac{1}{2}(x+\sin 6 x)+c}$

$\mathrm {\dfrac{1}{2}(x-\sin 6 x)+c}$

$\mathrm {\dfrac{1}{12}(6 x+\sin 6 x)+c}$

$\mathrm {\dfrac{1}{12}(6 x-\sin 6 x)+c}$