If for a sequence (tn), Sn = 2n2 +5n, find tn and show that the sequence is an A.P.
If for a sequence (tn), Sn = 2n2 +5n, find tn and show that the sequence is an A.P.
aishwarya , 8 Years ago
Grade 11
Algebra> If for a sequence (t n ), S n = 2n 2 +5n,...
1 Answers
Arun
Last Activity: 8 Years ago
As we know
For any sequence
Tn = Sn - S(n-1)
Hence
Tn = 2 n² + 5n - [2(n-1)² + 5(n-1)]
= 2n² + 5n - 2n² -2 +4n -5n +5
= 4n +3
Now
T1 = 7
T2 = 11
T3 = 15
Hence this forms an A.P.
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