Question

Find the sum of the first 7 terms of the series. 6-12+24-48+...

Answer 1

Answer: 258

Step-by-step explanation:

Since, the sum of GP is,

$S_{n}=\frac{a(r^n-1)}{r-1}$

where r is the common ratio,

a is the first term,

n is the number of term,

Here, series is, 6, -12, 24, -48, _ _ _ _

Which is a GP ( Because there is common ratio in the given consecutive terms )

So, for the above series,  a = 6, r = $\frac{6}{-12}=-2$  and  n = 7,

⇒ $S_{7}=\frac{6(-2^7-1)}{-2-1}$

⇒ $S_{7}=\frac{6(-128-1)}{-3}$

⇒ $S_{7}=\frac{6(-129)}{-3}$

⇒ $S_{7}=\frac{774}{3}=258$

Thus, the sum of the 7 terms of the given series is 258.

Answer 2

Answer: C is correct 258 i just took the test

Step-by-step explanation: