We shall now study three identities which are very useful in our work. These are obtained by multiplying a binomial by another binomial.
Let us consider the product
This is an identity, since the expression on the RHS is obtained from the LHS by actual multiplication. We may verify that for any value of a and any value of b, the values of two sides are equal.
The identities (I), (II) and (III) are known as standard Identities
Identity (IV) is the general form of the other three identities also.