to find the number of terms in arithmetical progression:

Let a=first term, d = common difference, l=t n =last term, s = required sum. Then, Writing the series in the reverse order, Adding together the two series, ..

) A sequence may be described by giving a formula for its n t h term. (iii) A sequence may be described by specifying its first few terms and a formula to determine the other terms of the sequence in terms of its proceeding terms. A sequence is said..

Quantities are said to be in Arithmetic progression when they increase or decrease by a common differenc..

Quantities are said to be in Arithmetic progression when they increase or decrease by a common differen..

A sequence of numbers is said to form a harmonic progression if their reciprocals form an arithmetic progression..

Geometric Progressions (G.P.) - The series of terms a, ar, ar 2 , ar 3 ,.... in which each term bears a constant ratio to the preceeding term is a geometric progression. The constant ratio is called the common ratio.OR A geometrical progression..

A sequence of numbers is said to form a harmonic progression if their reciprocals form an arithmetic progression..

1. If a, x, b are in A.P, then x is called the arithmetic mean (A.M.) between the extremes a and b. 2. a. To insert n arithmetic means between two given quantities. Let a and b be any two given quantities, and let A 1 ,A 2 ,A 3 ,-----A n be n arithmetic means to be ins..

If three quantities are in harmonic progression, then the middle quantity is called the harmonic mean between the other two. Example: 1/3, 1/7, 1/11 are in H.P., then 1/7 is the middle term. Hence 1/7 is the harmonic mean between 1/3 and 1/1..

i) 1.2 + 2.4 + 3.8 +.... to n terms The n t h term of (1,2,3,....n) is n. The n t h term of (2,4,8,...) is The n t h term of the given series is n2 n Subtracting (ii) from (i), we have ..