if the nth term of an AP is (2n+1), find the sum of the first n terms of the AP
Answers
Answered by
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Step-by-step explanation:
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.
Answered by
0
Answer:
Sn = n/2 [2a+(n-1)d]
Step-by-step explanation:
Sn = 2n+1/2 [2a+(2n+1-1)d]
= 2n+1 /2 [2a+2nd]
= 2n+1/2 * 2[a+nd]
= 2n+1 [a+nd]
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