The perimeter of a regular polygon = number of sides × length of one side

The perimeter of a square = 4 × side

Perimeter of rectangle = 2 × (l + b)

(where l and b denote the length and breadth respectively of the rectangle)

Area of a square = side × side

Area of a rectangle = l × b

**Triangles as Parts of Rectangles**

The sum of the areas of the two triangles, into which a diagonal of a rectangle divides the rectangle, is the same as the area of the rectangle. Also, both the triangles are equal in area.

**Generalising for Other Congruent Parts of Rectangles**

If we divide a rectangle into two congruent parts so that the area of one part is equal to the area of the other part, then

area of each congruent part = \(\frac { 1 }{ 2 }\) (the area of the rectangle)

Area of parallelogram = base × corresponding height (altitude)

**Conversion of Units**

1cm =10 mm

1 cm^{2} = 100 mm^{2}

1 m^{2} = 100 × 100 = 10,000 cm^{2}

1 km^{2} = 1000 × 1000 = 1,000,000 m^{2}

1 hectare = 10,000 m^{2}

Perimeter of square = 4 × side

Perimeter of Rectangle = 2 × (length + breadth)

Perimeter of triangle = sum of all sides of triangle = a + b + c

Area of square = side × side = (side)^{2}

Area of Rectangle = Length × Breadth = l × b

Area of Triangle = \(\frac { 1 }{ 2 }\) × Base × Height (Altitude)

Area of a parallelogram = Base × Height

The distance around a circular region is known as its circumference.

Circumference of a circle = πd = π(2r) = 2πr. where d is diameter and r is the radius.

Area of a circle = πr^{2}

π = \(\frac { 22 }{ 7 }\) or 3.14 (approximately).