This is an arithmetic progression based question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise – 9.6
In this question we have been given the arithmetic progression whose term is given by 5-6n . Also we have to find the sum of it.
CBSE DHANPAT RAI PUBLICATIONS
Understanding CBSE Mathematics
Class :- 10th
Question no 3
Given A.P. has nth term, an = 5 – 6n
Putting n = 1, we get a, first term of the A.P.,
a = 5 – 6(1) = -1
Sum of n terms of A.P. = Sn = n[a + an]/2
= n[-1 + (5 – 6n)]/2
= n(4 – 6n)/2 = n(2 – 3n)
Hence, the sum of the n terms of A.P. is n(2 – 3n).