Nov. 12, 2019

Multinomial Theorem:


Multinomial Theorem 

If we wish to expand (x+y+z)n, where n is a positive integer and x, y, z are complex numbers, we will follow the way given below: 

Step I We will substitute (y+z) = a. 

Step II We will expand the Binomial (x+a)n.

Step III Expand a (y+z)r () in each term of the Binomial Expansion (x+a)n.

Hence, In General, if the multinomial expression is of the form then its expansion can be written as

such that, are all +ve integers, and 

Problem Solving Trick 

Binomial as a special case of Multinomial 

If we have only two terms in multinomial expression rather than having m (multiple) value, the expansion in that can will be written as under 


which the equivalent form of Binomial Theorem (x+a)n.

Properties of Binomial Coefficients 

P-1 If then 

either r = s or r + s = n

P-2 Greatest Value of

is greatest if r =





Reasoning: Since, substituting x= 1, we have

P-7 In the expansion of (1+x)n the sum of even coefficients equals the sum of odd coefficients.

Reasoning: Since, substituting x = -1, we have 


Reasoning: Since, {using P-6}

Also, {using P-7}

Combining, we have


Reasoning: Since,

Differentiating w.r.t. x, we have 


Now, putting x = 1, we have 


Reasoning: Put x = -1 in equation (1) of the last property