If in an AP a =9, d= 7, Sn =495, find n and an quick plz
Answers
Answered by
11
Answer:
n = 110
Step-by-step explanation:
Sn = 495
Sn = n/2[2a+(n-1)d]
Given a = 9 , d = 7 , n = ?
495 = n/2[2(9)+(n-1)(7)]
990 = n(18+7n-7)
990 = n(7n+11)
7n^2+11n-990 = 0
7n^2+2n+9n-990=0
n(7n+2)+9(n-110)=0
(n+9)(7n+2)(n-110)=0
n=-9,-2/7,110
n can only be positive therefore n = 110
Answered by
5
Answer:
a110 = 772
Step-by-step explanation:
a110 = a+109d
=9+109x7
=9+763
=772
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