Question

if an atom of an ap is 2n + 1 what is the sum of the first three terms

Answer 1

Answer:

n th term l = 2n+1 (given)-----(1)

If we put n=1,we get first term of an A.P.

Then first term a=2(1)+1

a=3;-----(2)

Now we can find out sum of first n terms using this formula

sum of n terms of an A.P.=n/2(a+l)

(Here a is first term of an A.P. and l is last or nth term of A.P.)

Values of a and l putting in the equation (3) from (2) and (1)

Sum of first n terms of an A.P.=n/2(3+2n+1)

=> n/2(2n+4)

=> n(n+2)

Finally, sum of first n terms of an A.P. is n(n+2) Ans.

hoping it will help you

Answer 2

what is atom??
if it is a term..

term of an ap=2n+1

first term=2(1)+1
=2+1 = 3
second term= 2(2)+1
=4+1=5

third term=2(3)+1
=6+1=7

the sum of first three terms=3+5+7=15
hope it is useful