Sn = 990 , A = 2 , d = 5 , n = ?
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Answered by
0
Answer:
n=99
Step-by-step explanation:
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Answered by
1
Answer:
Sn=n/2[2A+(n-1)d]
990=n/2[4+5n-5]
1980=5n²-n
5n²-n-1980=0
by using quadratic formula
n=20
cross check:
putting value of n
=20/2[4+95]
=10[99]
=990
that is equal to Sn
hence n=20 is right
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