Page 163 - Maths Class 06

s
2. The perimeter of a square = ´4 side
= 4s s s
Where s is a vari able that represents the side. s
l
3. The perimeter of a rectangle = ´2 length + ´2 breadth

= 2l + 2b b b
The rule therefore is, the perimeter of rectangle is 2l + 2b l
where l b, represent length and breadth respectively.

4. The perim eter of a regular polygon can be generalized as,

Perim eter of a regular polygon = ´n side
= ´n s

Where n = number of sides and s = the measure of the side.
Rules from Arithmetic

We have learnt in earlier chapters about the properties of whole numbers over addition, subtraction and
multiplication.
These properties hold true for all whole numbers and thus are generalized using variables.
1. Commu ta tive prop erty of addi tion

If a b, are two whole numbers, then a b+ = b a+
2. Commu ta tive prop erty of multi pli ca tion
If a b, are two whole numbers, then a b´ = b a´

3. Asso cia tive prop erty of addi tion
If a b, and c are any three whole numbers, then (a b+ ) c+ = + (b c+ )
a
4. Asso cia tive prop erty of multi pli ca tion

If a b, and c are any three whole numbers, then (a b´ ) c´ = a´ (b c´ )
5. Distrib u tive prop erty of multi pli ca tion over addi tion

If a b, and c are any three whole numbers, then a´( b c+ ) = a b a c´ + ´
EXAM PLE : A cube is a three-dimen sional figure. It has six faces and all of them are iden ti cal squares.
The length of an edge of the cube is given by a. Find the formula for the total length of the
edges of a cube.
SOLUTION : A cube has 12 edges,
Each edge is same in length say, a then

The total length of edges = 12 a
´
a
= 12a
Algebraic Expression and Its Formation

An algebraic expression contains variables and a constant. It cannot be evaluated as such unless we know
the value of the variables.

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