an=4,d=2,sn=-14 find n and a
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Answered by
4
Answer:
A=-8 N=7
Step-by-step explanation:
a n =a+(n−1)d
4=a+(n−1)2
4=a+2n−2
6=a+2n
∴a=6−2n...(1)
S n = 2 n
[2a+(n−1)d]
−14= 2 n
[2(6−2n)+(n−1)2]
−28=n[12−4n+2n−2]
−28=12n−2n 2 −2n
−28=10n−2n 2
−14=5n−n 2
Solving the above equation, we get,
(n−7)(n+2)=0
n=7,−2
∴n=7
a=6−2n From (1)
a=6−2(7)=−8
Answered by
3
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