If $y=A \cos \mathrm{n} x+\mathrm{B} \sin \mathrm{nx}$, then $\frac{\mathrm{d}^2 y}{\mathrm{~d} x^2}=$

A man and his wife appear for an interview for two posts. The probability of the husband's selection is $\frac{1}{7}$ and that of the wife's selection is $\frac{1}{5}$. If they appear for the interview independently, then the probability that only one of them is selected, is

The expected value of the sum of the two numbers obtained on the uppermost faces, when two fair dice are rolled, is

$$\int \tan ^{-1}\left(\frac{1-\sin x}{1+\sin x}\right) d x=$$