This is the Important question based on Arithmetic progression Chapter of R.S Aggarwal book for ICSE & CBSE Board.
Here the nth term of AP is given
you have to find the
(i) Sum of Given first n terms of the AP
(ii)Sum of n terms of the AP
Question Number 23 of Exercise 11 C of RS Aggarwal Solution
Deepak BoraNewbie
If the nth term of an AP is (4n+1) find the sum of the first 15 terms of the AP. Also find the sum of its n terms.
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The a_n term of the AP is given
=(4n+1)
so that a_1 is :
a_1=4(1)+1
a_1=5
The Sum of first 15 terms of the AP is :
S_15=n/2[a_1+a_15]
S_15=15/2[5+4(15)+1]
S_15=15/2[5+61]
S_15=15/2×66
S_15=495
the sum of first 15 term is 495
The sum of n Terms of the AP is:
S_n=n/2[a_1+a_n]
S_n=n/2[5+4n+1]
S_n=n/2[6+4n]
S_n=n[3+2n]
the sum of n terms of the AP is n[3+2n]