Question

Find the sum of first 10 terms of the G.P 3, 6, 12, 24 ..........

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Answer 1

a = 3

r = 2

Sum of n terms $S_n$ = $\frac{a(r^n-1)}{r-1}$

$S_{10}$ = $\frac{a(r^{10}-1)}{r-1}$

= $\frac{3(2^{10}-1)}{2-1}$

$=(1024-1)\times 3$

$=1023\times 3$

= 3069