Question

The sum of the first 20 terms of the progression 3 6 12 is

Answer 1

The given progression:

3, 6, 12, ...... are in GP.

Here, first term (a) = 3, common ratio (r) = $\dfrac{6}{3}$ = 2 and the number of terms(n) = 20

We have to find, the sum of the first 20 terms of the given progression.

Solution:

We know that,

The sum of the first n terms of the GP

$S_{n} =\dfrac{a(r^n-1)}{r-1}$, Here r > 1

∴ The sum of the first 20 terms of the given progression

$S_{20} =\dfrac{3(2^{20}-1)}{2-1}$

⇒ $S_{20}$ = $\dfrac{3(2^{20}-1)}{1}$

⇒ $S_{20}$ = $3(2^{20}-1)$

∴ The sum of the first 20 terms of the given progression, $S_{20}$ = $3(2^{20}-1)$

Answer 2

Step-by-step explanation:

1/2

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