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Plane figures A Plane is a flat surface with no thickness. Our world has three dimensions, but there are only two dimensions on a Plane. Examples: length and height, or x and y and it goes on forever. A plane is a flat or level surface in two dimensions. Figures such as circles or squares have all of their parts lying on a plane and thus, are examples of plane figures.

Some Plane Figures

TRIANGLE A triangle is a closed plane figure bounded by three line segments. E.g. ABC is a triangle having three sides and three interior angles. The symbol for a triangle is. So triangle ABC is written as ABC. The area A of a triangle is A=1/2 b*h Where b = base and h = vertical height

Area of a triangle 1. Take a piece of paper and divide the whole paper into squares of side 1 cm by drawing lines. 2. Draw a triangle LMN on this paper. 3. Now, count the number of complete squares and denote it by x. 4. Now count the number of half squares and denote it by y. 5. Count the number of squares which are more than half and denote it by z. 6. Leave those squares which cover less than half. 7. Area of LMN = (x+ ½y + z) cm

Area of LMN = (4+1/2(0) +4) cm2 = (4+0+4) cm2 = 8 cm2

RECTANGLE A rectangle is a four-sided closed shape where every angle is a right angle (90°). Also opposite sides are parallel and of equal length. The area A of a rectangle (a bit more general) is the product of the length b of a long side (``base or breadth'') and the length h of a short side (``height''): A = b*h.

Area of a rectangle The steps to calculate area of rectangle of length 6 cm and breadth 3 cm are as follows:1. 2. 3. 4.

Divide the rectangle ABCD into squares of side 1cm each. Now count the number of squares. There are 18 squares in whole rectangle. Now area of 1 square:-

=Side * Side =1 * 1 cm2 =1 cm2 Area of 18 squares= 18 * 1 =18 cm2 The area of rectangle ABCD =18 cm2