Find the sum of first 15 terms of an AP whose 4th and 9th terms are -15 and -30 respectively.
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Answered by
1
Answer:
Step-by-step explanation:
a=1,l=11,S
n
=36
S
n
=
2
n
(a+l)
36=
2
n
(1+11)
⇒36=
2
n
×12
⇒36=6n
⇒n=6
Answered by
4
Answer:
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