Question

2. If the sum of the first 12 terms of a geometric series is 8190 and the common ratio is 2. Find the first term and the 20th term

Answer 1

the first term is 2 and the 20th term is 1048576 .

Step-by-step explanation:

Here we have , If the sum of the first 12 terms of a geometric series is 8190 and the common ratio is 2. We need to Find the first term and the 20th term. Let's find out:

We know that Sum of a GP is :

⇒ $S_n = \frac{a(r^n-1)}{r-1}$

So ,Sum of first 12 terms is :

⇒ $S_1_2 = \frac{a(2^{12}-1)}{2-1}$

⇒ $8190=a(2^{12}-1)$

⇒ $\frac{8190}{4095}=a$

⇒ $a=2$

Now , nth term of a GP is

⇒ $a_n = ar^{n-1}$

So , 20th term is :

⇒ $a_2_0 = 2(2)^{20-1}$

⇒ $a_2_0 = (2)^{20}$

⇒ $a_2_0 = 1048576$

Therefore , the first term is 2 and the 20th term is 1048576 .