Скачать или смотреть Class 8th Maths | Algebraic Expressions and Identities | Exercise 9.1 Question 1-2

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:
(I) (a + b)² = a² + 2ab + b²
(II) (a – b)² = a2²– 2ab + b²
(III) (a + b) (a – b) = a² – b²
12. Another useful identity is (x + a) (x + b) = x² + (a + b) x + ab
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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