Class-VII Maths

ALGEBRAIC EXPRESSIONS

PRESENTED BY:-

Amit Ranjan

JNV, Cooch-Behar, W.B.

INTODUCTION

• An Algebraic Expression is the combination of constant and variables. We use the operations like addition, subtraction etc. to form an Algebraic expression.
• Variable A variable does not have a fixed value .it can be varied. It is represented by letters, like a, x, y, p, m etc.
• Constant A constant has a fixed value. Any number without a variable is a constant.

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Example 2x + 7

Here we got this expression by multiplying 2 and x and then add 7 to it.

In the above expression, the variable is x and the constant is 7.

Terms of an Expression�

• Terms To form an expression we use constant and variables and separate them using the operations like addition, subtraction etc. these parts of expressions which we separate using operations are called Terms.

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In the above expression, there are three terms, 4x, - y and 7.

Factors of a Term�

• Every term is the product of its factors. As 4x + 5 is an expression, here the term 4x is the product of 4 and x. So 4 and x are the factors of that term.

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We can understand it by using a tree diagram.

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• Coefficients

As you can see above that some of the factors are numerical and some are algebraic i.e. contains variable. The numerical factor of the term is called the numerical coefficient of the term.

In the above expression, -1 is the coefficient of ab

2 is the coefficient of b² -3 is the coefficient of a².

Parts of an Expression�

Here in the above figure, you can identify the terms, variables, constants and coefficients.

Like and Unlike Terms�

LikeTerms are the terms which have same algebraic factors. They must have the same variable with the same exponent.

UnlikeTerms are the terms which have different algebraic factors.

• 2x² + 3x – 5 does not contain any term with same variable.

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• 2a² + 3a² + 7a – 7 contains two terms with same variable i.e. 2a² and 3a².so these are like terms.

Classification of Algebraic Expressions

Addition and Subtraction of Algebraic Expression�

Addition of Like Terms

If we have to add like terms then we can simply add their numerical coefficients and the result will also be a like term.

Example: |Add 2x and 5x.

Solution: 2x + 5x = (2 × x) + (5 × x)

= (2 + 5) × x (using distributive law)

=7 × x = 7x

Subtraction of Like Terms

If we have to subtract like terms then we can simply subtract their numerical coefficients and the result will also be a like term.

Example: Subtract 3p from 11p.

Solution: 11p – 3p = (11-3) p

= 8p

Addition of unlike terms

If we have to add the unlike terms then we just have to put an addition sign between the terms.

Example: Add 9y, 2x and 3

Solution: We will simply write it like this 9y + 2x + 3

Subtraction of Unlike Terms

If we have to subtract the unlike terms then we just have to put minus sign between the terms.

Example: Subtract 9y from 21.

Solution: We will simply write it like this 21 - 9y

SIMPLIFICATION

To SIMPLIFY algebraic expressions, we have to arrange them so that the like terms come together, then simplify the terms and the unlike terms will remain the same in the resultant expression.

Example: Simplify the expression: 12p² – 9p + 5p – 4p² – 7p + 10

Solution: First we have to rearrange the terms.

12p² – 4p² + 5p – 9p – 7p + 10 = (12 – 4) p² + (5 – 9 – 7) p + 10

= 8p² + (– 4 – 7) p + 10

= 8p² + (–11) p + 10

= 8p² – 11p + 10

While subtracting the algebraic expression from another algebraic expression, we have to arrange them according to the like terms then subtract them.

Subtraction is same as adding the inverse of the term.

Example: Subtract 4ab– 5b² – 3a² from 5a² + 3b² – ab

Solution

Finding the Value of an Expression�

Example: Find the value of the expression 2x + 7 if x = 3.

Solution: We have to put the value of x = 3.

2x + 7 = 2(3) + 7

= 6 + 7

= 13

Expressions with One Variable

Example: Find the value of y² + 2yz + z² if y = 2 and z = 3.

Solution: Substitute the value y = 2 and z = 3.

y² + 2yz + z² = 2² + 2(2) (3) + 3²

= 4 + 12 + 9 = 25

Expressions with more than one variables

Formulas and Rules using Algebraic Expression�

There are so many formulas which are made using the algebraic expression.

Perimeter Formulae

• The perimeter of an equilateral triangle = 3L where L is the length of the side of the equilateral triangle. Here L is variable which can be varied according to the size of the equilateral triangle.
• The perimeter of a square = 4L where L is the length of the side of the square.
• The perimeter of a regular pentagon = 5L where L is the length of the side of the Pentagon.

Area formulae

• The area of the square = a²  where a is the side of the square
• The area of the rectangle = L × b = Lb where the length of a rectangle is L and its breadth is b
• The area of the triangle = 1/2 × b × h where b is the base and h is the height of the triangle. Here if we know the value of the variables given in the formulas then we can easily calculate the value of the quantity. 

Rules for the Number Pattern�

• If we denote a natural number by n then its successor will always be (n + 1).

If n = 3 then n + 1 will be 3 + 1 = 4.

• If we denote a natural number by n then 2n will always be an even number and (2n + 1) will always be an odd number. If n = 3 then 2n = 2(3) = 6(even number), n = 3 then 2n + 1 = 2(3) + 1 = 7 (odd number)
• If we arrange the multiples of 5 in ascending order then we can denote it by 5n. If we have to check that what will be the 11^th term in this series then we can check it by putting n = 11 in 5n. So, 5n = 5(11) = 55.

Pattern in geometry

The number of diagonals which we can draw from one vertex of any polygon is (n – 3) where n is the number of sides of the polygon.

How many diagonals can be drawn from the one vertex of a octagon?

The number of sides in a octagon is 8 so (n - 3) = (8 - 3) = 5.

Thank you

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Amit Ranjan

TGT- Maths

JNV, Cooch-Behar, W.B.

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