19. Find the sum of first 15 terms of 3 +6+ 9. using the formula
Answers
Answered by
3
Answer:
360
Step-by-step explanation:
Formula used is n/2[2*a+(n-1)*d]
where
n is the number of terms
a is the first term
d is the difference between first and second term
Answered by
0
Answer:
Here, a=3,r=
T
1
T
2
=
3
6
=2,n=6
S
n
=
r−1
a(r
n
−1)
[∵r>1]
S
6
=
2−1
3[2
6
−1]
=
1
3[64−1]
=3×63 ∴S
6
=189
Step-by-step explanation:
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