12.Algebraic Expressions

Sumedha Collage - Gampaha

Grade 7

Mathematics

New words in this lesson

Algebraic

Expressions

Unknown constant

Variable

Terms

Like terms

Coefficient

Unlike terms

Substitute

Sub Topics,

1. Constructing algebraic expressions

2. Constructing algebraic expressions having two unknown terms

3. Simplifying the terms of an algebraic expression

4. Substituting values for the unknowns in an algebraic expression

1. Constructing algebraic expressions

When we are don’t know the actual value in mathematical

expression , we can use “x” to replace that

x is the “unknown constant ” or “variable”

What is an Unknown constant

when the numerical value of a constant amount is not

known, it is defined as an “unknown constant”.

Eg:- The amount of the beverage bottle

The amount of the ink filled in to a pen

Not only the simple “x” we can use

simple letters of the English alphabet such as

a,b,c,…,x,y,z are used to represent unknown

constants and variables.

What is an variable

Different values depending on its defined as a “variable”.

Eg:- Daily income of a shop

There are x number of pens in a pencil case and Kamal gives 2

pencils to his friend.

Write the remaining number of pens in the pencil case as an

algebraic expression.

a - 2

algebraic expression

a and 2 are defined as the “terms” of this expression.

2. CONSTRUCTING

ALGEBRAIC EXPRESSIONS

HAVING TWO

UNKNOWN TERMS

Example :-

The price of a pencil is x rupees and the price of an eraser is y rupees.

Let us write the price of 5 pencils and 2 erasers as an algebraic

expression.

The price of 2 erasers and 5 pencils =

price of a pencil = x

price of an eraser = y

2x 5y+

2x + 5y

3. SIMPLIFYING THE TERMS OF AN ALGEBRAIC

EXPRESSION

The price of an orange is a rupees. Nimal bought 5 oranges

and Deepani bought 8

What is the total amount spent =

a5 ×

5𝑎

a8 ×

8𝑎

?5𝑎 + 8a

= 13a Like terms

* like terms can Simplify

Simplify 4x + 3y + 2x + 2y.

= 4x + 2x + 3y + 2y (like terms )

= 6x + 5y

Simplify 4x + 3y + z

(Unlike terms )

Coefficient

4.SUBSTITUTING VALUES FOR THE UNKNOWNS IN AN

ALGEBRAIC EXPRESSION

4x + 3y - 2

= 4(4) + 3(2) - 2

Find the value of the algebraic expressions given

below when, x = 4 and y = 2.

= 16 + 6 - 2

= 22 - 2

= 20

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