MCQ
If ${a_{1,}}{a_2},{a_3}.....,{a_n}$ is an $A.P.$ with common difference d then $\tan \left[ {{{\tan }^{ - 1}}\left( {\frac{d}{{1 + {a_1}{a_2}}}} \right) + {{\tan }^{ - 1}}\left( {\frac{d}{{1 + {a_2}{a_3}}}} \right) + ...} \right.$ $\left. { + {{\tan }^{ - 1}}\left( {\frac{d}{{1 + {a_{n - 1}}{a_n}}}} \right)} \right] = $
- A$\frac{{(n - 1)d}}{{{a_1} + {a_n}}}$
- ✓$\frac{{(n - 1)d}}{{1 + {a_1}{a_n}}}$
- C$\frac{{nd}}{{1 + {a_1}{a_n}}}$
- D$\frac{{{a_n} - {a_1}}}{{{a_n} + {a_1}}}$