42. a=10. d = 6 , a_{n} = 100 given then find n and Sn
Answers
Answered by
2
Answer:
Ans: A = 6 - 2(7) = -8.
Step-by-step explanation:
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
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Answered by
8
Answer:
a+(n-1)d = An
10+ (n-1)6=100
(n-1)6=100-10
(n-1)=90/6
n-1=15 , n=15+1=16
value of n is 16
Sn= n/2(2a+(n-1)d
Sn= 16/2(2×10+(16-1)6
Sn= 8 ×55 = 880
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