Question

The sum of the first n terms of an AP is 5n²-3n . Find the AP and hence find its 15th term​

Answer 1

Answer:

142

Step-by-step explanation:

Sn=5n²-3n

Putting n=1, 5n²-3n

=5-3=2

Putting n=2, 5n²-3n

=14

Therefore 2nd term is 14-2=12

Therefore AP is 2, 12, 22 ... and so on.

nth term = a+(n-1)d

15th term=a+14d

=2+14*10

=2+140

=142

Answer 2

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AP:2,12,22

92

a10=92

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Sum of the n terms of an A.P. is

5n2 - 3n.

Find the terms of the A.P. and also find the 16th term.

Sn = 5n2 - 3n

an = Sn - Sn - 1

an = 5n2 - 3n - [5(n - 1)2 - 3 (n - 1)]

an = 5n2 - 3n -[5(n2 - 2n + 1) - 3n + 3]

an = 5n2 - 3n - 5n2 + 10n - 5 + 3n - 3

an = 10n - 8

a1 = 2

a2 = 20 - 8 = 12

a3 = 30 - 8 = 22

a10=100-8=92

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