$\mathrm{If} 2^{10} + 2^9 . 3^1 +\hspace{0.17em}{2}^8 . 3^2 +\hspace{0.17em}... + 2 . 3^9 +3^{10} = 3^{10}= \mathrm{S} - 2^{11} \mathrm{Then} \mathrm{S} = ?$

• $3^{11}$

• $2 . 3^{11}$

• $\frac{3^{11}}{2} + 2^{10}$

• $3^{11} - 2^{11}$

If the sum of the second,third and fourth terms of a positive term G.P. is 3 and the sum of its sixth, seventh and eighth terms is 243, then the sum of the first 50 terms of this G.P. is :

• $\frac{2}{13}\left(3^{50} - 1\right)$

• $\frac{1}{26}\left(3^{49} - 1\right)$

• $\frac{1}{13}\left(3^{50} - 1\right)$

• $\frac{1}{26}\left(3^{50} - 1\right)$

213.

If the sum of the first 20 terms of the series log$\left({\log }_{\left(7^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}\right)}\left(\mathrm{x}\right)\right) + \left({\log }_{\left(7^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$3$}\right.}\right)}\left(\mathrm{x}\right)\right) + \left({\log }_{7^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}}\left(\mathrm{x}\right)\right) + ... \mathrm{is} 460$,

then x = ?

• e²

• $7^{\raisebox{1ex}{$46$}\!\left/ \!\raisebox{-1ex}{$21$}\right.}$

• 7²

• $7^{\raisebox{1ex}{$1$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}$

Let a , b, c, d and ay non zero distinct real numbers such that (a² + b² + c²)p² – 2(ab + bc + cd)p + (b² + c² + d²) = 0. Then :

• a, b, c, d are in A.P.

• a, c, p are in G.P.

• a, b, c, d are in G.P.

• a, c, p, are in A.P.