# CBSE, Class VIII, Mathematics Algebraic Expressions and Identities

Click below for Class 8 Algebraic Expressions and Identities NCERT solutions, Exemplar Solutions, worksheets and assignments, NCERT books, MCQs, easy to learn concepts and study notes and other study material

1. Expressions are formed from variables and constants.

2. Terms are added to form expressions. Terms themselves are formed as product of factors.

3. Expressions that contain exactly one, two and three terms are called monomials, binomials and trinomials respectively. In general, any expression containing one or more terms with non-zero coefficients (and with variables having non- negative exponents) is called a polynomial.

4. Like terms are formed from the same variables and the powers of these variables are the same, too. Coefficients of like terms need not be the same.

5. While adding (or subtracting) polynomials, first look for like terms and add (or subtract) them; then handle the unlike terms.

6. There are number of situations in which we need to multiply algebraic expressions: for example, in finding area of a rectangle, the sides of which are given as expressions.

7. A monomial multiplied by a monomial always gives a monomial.

8. While multiplying a polynomial by a monomial, we multiply every term in the polynomial by the monomial.

9. In carrying out the multiplication of a polynomial by a binomial (or trinomial), we multiply term by term, i.e., every term of the polynomial is multiplied by every term in the binomial (or trinomial). Note that in such multiplication, we may get terms in the product which are like and have to be combined.

10. An identity is an equality, which is true for all values of the variables in the equality. On the other hand, an equation is true only for certain values of its variables. An equation is not an identity.

11. The following are the standard identities:

(a + b)^{ 2} = a^{2} + 2ab + b^{2} (I)

(a – b) ^{2} = a^{2} – 2ab + b^{2} (II)

(a + b) (a – b) = a^{2} – b^{2} (III)

12. Another useful identity is (x + a) (x + b) = x^{2} + (a + b) x + ab (IV)

13. The above four identities are useful in carrying out squares and products of algebraic expressions. They also allow easy alternative methods to calculate products of numbers and so on.

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