Question

The sum of first four terms of the G.P. 2, 6, 18, ....., is ______.

विकल्प

• 26

• 80

• 160

• 52

Answer 1

The sum of first four terms of the G.P. 2, 6, 18, ....., is 80.

Explanation:

By formula,

Common ratio = `(a_n+1)/(a_n)`

r = `6/2` = 3.

By formula,

⇒ a_n = ar^{n − 1}

⇒ a₄ = 2 × (3)^{4 − 1}

⇒ a₄ = 2 × 3³

⇒ a₄ = 2 × 27 = 54

Sum of first four terms of G.P. = 2 + 6 + 18 + 54 = 80