Solving a binomial Using The Pascal's Triangle

The Pascal s triangle is to some extent useful in expanding a binomial. Before I go on, let me explain what a binomial is. A binomial could be defined as a mathematical expression of two terms which usually involves addition and subtraction. Examples are (y-1), (x+a)^2, (x-3)^3.


The Pascal s triangle makes the expansion of binomials with high powers easier and faster. The Pascal s triangle for a binomial with increasing power is the pattern of coefficient of the binomial as its power increases from a lower value to a higher value. It is best explained using an example. Lets take a binomial (x+1) increasing in power from (x+1)^1 to (x+1)^2 to (x+1)^3 on and on like that till we reach (x+1)^6 we have a pattern like the one below.



Binomial                                                                coefficient

(x+1)^1                                                                      1   1



(x+1)^2                                                                     1  2  1



(x+1)^3                                                                   1   3  3   1



(x+1)^4                                                                1   4   6   4    1



(x+1)^5                                                           1     5   10  10   5    1



(x+1)^6                                                       1    6    15    20  15    6    1.



This pattern of coefficients is what mathematicians commonly refer to as the Pascal s triangle. It is the same for all binomials. Pascal s triangle can be derived or was derived by a french philosopher called Pascal. For how it can be derived see Pascal s triangle.
 
Now let us give an example. Expand (y-1)^3.

Solution.

First of all we look at the power to which the binomial is raised which is 3.

Next we go to the Pascal's triangle and see the coefficients that correspond to a binomial raised to the power of 3 which are 1 3 3 1.

So (y-1)^3=1+3+3+1.

Next we identify the first and second terms which are y and -1 respectively.

Futhermore, we then multiply the first and second terms to the coefficients but know that the powers of the first term y decrease from the power of the binmial to 0 going from left to right while that of -1 increase from 0 to that of the binomial. See Pascal's triangle and binomial.

So (y-1)^3= 1(y)^3(-1)^0+3(y)^2(-1)^1+3(y)^1(-1)^2+1(y)^0(-1)^3
(y-1)^3= y^3-3y^2+3y-1