SEQUENCE: A succession of numbers formed and arranged in a definite order according to a certain definite rule is called sequence.
The number occuring at the nth place of sequence is called its nth term or the general term, to be denoted by
SERIES: By adding the terms of a sequence, we obtain a series.
A series is finite or infinite according as the number of terms added is finite or infinite
PROGRESSION: Sequence following certain patterns are called progressions. we will discuss about two types of progressions, namely arithmetical and geometrical.
ARITHMETICAL PROGRESSION(A.P.): it is a sequence in which each term , except the first one, differs from its preceding term by a constant, called the common difference.
in an A.P. we usually denote the first term by a, common difference by d and the nth term by . clearly, d=().