sequence and series Flashcards
1
Q
nth term of ap
A
a+(n-1)d
2
Q
nth term from end
A
L-(N-1)D
3
Q
sum of n terms
A
n/2*{2a+(n-1)d}
from last term , n/2*{a+l}
4
Q
3no. are in ap
A
2b=a+b
5
Q
nth term of gp
A
ar^n-1
6
Q
nth term from end (GP)
A
L/r^n-1
7
Q
sum of first n terms (gp)
A
a(1-r^n/1-r) ,r not equal to 1
na r=1
8
Q
sum of infinite GP
A
a/1-r
9
Q
3 no. are in gp
A
b^2=AC
10
Q
condition for a,b,c being in gp as well as Ap
A
a=b=c
11
Q
sum of first n natural no.
A
n(n+1)/2
12
Q
sum of squares
A
n(n+1)(2n+1)/6
13
Q
sum of cubes
A
[n(n+1)^2//2]^2`
14
Q
sum of even no.
A
n(N+1)
15
Q
sum of odd no.
A
n^2
