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Question -

The sum of n terms of the G.P. 3, 6, 12, тАж is 381. Find the value of n.



Answer -

Given:

Sum of GP =┬а381

Where, a = 3, r = 6/3= 2, n = ?

By using the formula,

Sum of GP for n terms= a(rn┬атАУ 1 )/(r тАУ 1)

381 = 3 (2n┬атАУ1)/ (2-1)

381 = 3 (2n┬атАУ1)

381/3 = 2n┬атАУ1

127 = 2n┬атАУ1

127 + 1 = 2n

128 = 2n

27┬а= 2n

n = 7

тИ┤ value of n is 7

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