Question

Find the sum of the first seven terms of the sequence 4, 12, 36, 108, … .

Answer 1

The given sequence is 4,12,36,108....

Here we can observe the first term $a_{1}$ = 4 , $a_{2}=12$ and so on.

The common ratio (r)=$\frac{12}{4}=3$

Since the common ratio is greater than 1,

Therefore the sum of the geometric series = $\frac{a(r^{n}-1)}{r-1}$

Since we have to find the sum of first seven terms, so n=7

=$\frac{4(3^{7}-1)}{3-1}$

=4372.

Therefore, option C is the correct answer.