NCERT Class 8 Mathematics Chapter 9 Algebraic Expressions and Identities CBSE Board Sample Problems
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Algebraic Expressions and Identities
Algebraic Expressions is the expression having constants and variable. It can have multiple variable and multiple power of the variable
Example
Some Important Points on Algebraic Expressions
Terms  Description 
Terms factors  Terms are added to form expressions terms themselves can be formed as the product of factors 
Coefficient  The numerical factor of a term is called its numerical coefficient or simply coefficient 
Monomial  Algebraic expression having one terms is called monomials Example 3x 
Binomial  Algebraic expression having two terms is called Binomial Example 
Trinomial  Algebraic expression having three terms is called Trinomial Example 
Polynomial  An expression containing, one or more terms with nonzero coefficient (with variables having non negative exponents) is called a polynomial 
Like terms  When the variable part of the terms is same, they are called like terms 
Unlike terms  When the variable part of the terms is not same, they are called like terms 
Operation on Algebraic Expressions
S. no  Operation  Descriptions 
1.  Addition  ϖ We write each expression to be added in separate row, while doing so we write like terms one below the other Or We add the expression together on the same line and arrange the like term together ϖ Add the like terms ϖ Write the Final algebraic expression 
2.  Subtraction  ϖ We write each expression to be subtracted in a separate row, while doing so we write like terms one below the other and then we change the sign of the expression which is to be subtracted i.e. +becomesandbecomes+ or We subtract the expression together on the same line, change the sign of all the term which is to be subtracted and then arrange the like term together ϖ Add the like terms ϖ Write the Final algebraic expression 
3.  Multiplication 

What is an identity?
An identity is an equality, which is true for all values of the variables in the equality.