Arithmetic and geometric progression

While dealing with mathematics few terms always make us tensed. Arithmetic progression and geometric progression are few.

Arithmetic progression is also called arithmetic sequence. A sequence or progression is a group of number or letters arranged in an order. These terms are generally denoted as a1, a2, a3........an.
The suffix denotes the location of the term.

Arithmetic progression is that sequence where the sequence begins with a and then each term is found by adding the common difference d. As for example: a, a+d, a+2d, a+3d....

Geometric progression on the other hand is a sequence where each term except the first term can be can be calculated by multiplying the preceding term by a constant term or a common ratio. As for example: a, ar2, ar3.....

There is another progression in mathematics which is known as harmonic progression but basic math is confined basically to these two progression.