Question

Find the sum of the geometric series: $1+4+16+64+......9$ terms.

• A. $57381$
• B. $67381$
• C. $77381$
• D. $87381$

Answer 1

The correct option is D $87381$

Given series is $1+4+16+64+.....9$ terms

Here $a=1,r=4$
We know $S_n=\frac{a_1(r^n-1)}{r-1}$
$=\frac{1(4^9-1)}{4-1}$

$=\frac{(4^9-1)}{3}$

$=87381$