Question

Find the seventh term of the geometric sequence $1,-3,9,-27,....$

• A. -243
• B. -30
• C. 81
• D. 189
• E. 729

Answer 1

The correct option is E 729

$n^{th}$ term of geometric sequence $=$$a_n=a_1\times (r{)}^{n-1}$

Where $a_1$ $=$ first term $,r=$ common ratio,$n=n^{th}$ term

Here $a_1=1.r=\frac{-3}{1}=-3,n=7^{th}$ term

$\Rightarrow a_7=1\times (-3{)}^{7-1}$

$\Rightarrow a_7=1\times (-3{)}^6$

$\Rightarrow a_7=729$