### Theory:

In the previous topics, we have learnt how to add, subtract, multiply and divide to combine variables and constants to frame the algebraic expressions.

Let us recall a few basic concepts about expressions.

1. What is a binomial expression?

An expression which contains only $$2$$ terms separated by operation addition or subtraction are called as binomial expression.

Consider the expression $$6y + 2$$. In this, the expression is obtained by multiplying the variable $$y$$ with the constant $$6$$ and then adding the number $$2$$ to the product.

Here, $$6y$$ is the variable term, $$y$$ is the variable, $$6$$ is the coefficient of $$y$$ and $$2$$ is the constant term.

2. What are like terms?

Terms which have the same variables are called as like terms.

The terms $$6y$$, $$3y$$, $$10y$$ are examples of like terms.

3. What are unlike terms?

Terms having different variables are called as unlike terms.

The terms $$-5x$$, $$-3y$$ are examples of unlike terms.
When we add or subtract like terms, we get a new term. But, when we add or subtract unlike terms, we get a new expression.

Consider adding the like terms $$3x$$ and $$4x$$, we get, $$3x + 4x = 7x$$.

Now, consider adding an unlike term $$6x$$ and $$2y$$, we get, $$6x + 2y$$.