Q. 184.4( 5 Votes )

If the sum of the

Answer :

We know that sum of n terms of an A.P. is given by,

Where a= first term, d= Common difference, n= No. of terms

3n2 + 7n=2an + (n-1)nd

3n2 + 7n=n2d + (2a-d)n

By comparing, we get






So, nth term of this A.P.,

An=a + (n-1)d=5 + (n-1)3=5 + 3n-3=3n + 2

So,nth term is given by (3n + 2)

Now,For 20th term, n=20

A20=3 × 20 + 2=62

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