Free Study Material For RRB Examination
Subject : Mathematics (Sequences & Series)
Arithmetic Progression (AP)
If three terms are in AP, then they can be taken as (a – d),
a, (a + d).
If four terms are in AP, then they can be taken as (a – 3d), (a
– d), (a + d), (a + 3d).
If five terms are in AP, then they can be taken as (a – 2d), (a
– d), a, (a + d), (a + 2d).
Geometric Progression (GP)
A geometric progression is a sequence in which terms increase or
decrease by a constant ratio called the common ratio.
(i) The sequence 1, 3, 9, 27, 81…is a geometric progression
whose first term is 1 and common ratio 3.
Harmonic Progression (HP)
If the reciprocals of the terms of a series form an arithmetic
progression, then the series is called a harmonic progression.