Area and Perimeter

The Area of a shape is nothing but the whole surface covered by the shape. The perimeter of a shape is the total boundary of the shape.

Here are some formulas of area and perimeter that you learned in previous grades.

• Area of a square = Side*Side

• The perimeter of a square = 4*Side

• Area of a rectangle = Length*Breadth

• The perimeter of a rectangle = 2(Length+Breadth)

• The perimeter of a triangle = a+b+c (sum of all the sides)

From classes 7 and 8 we start to learn the area and perimeter of a circle, parallelogram, trapezium, a general quadrilateral, and a triangle.

Circle:- A circle has a curved circumference, so finding the perimeter/circumference is tricky but easy when understood. We already know the parts of a circle. We can find the circumference with a special number called 'Pi'. Well, that's just what we call it but the number actually is - 3.1415926535......... and it goes on forever, hence we round it off to 3.14 or 22/7. The symbol for Pi is π.

• The Area of a circle = π*r*r or π*r(squared)

• The Circumference of a circle = π*2*r

Getting confused in the formula of a circle is normal but if you understand it you don't need any formula at all. Watch the below videos to understand completely about pi, area, and circumference of a circle:

youtu.be/cC0fZ_lkFpQ ; youtu.be/O-cawByg2aA

Parallelogram:- A parallelogram has parallel sides and looks just like a rectangle without those parallel sides. Like any other polygon, getting the perimeter of a parallelogram is easy. Just add the sides! And to get the area you need to understand it pictorially first.

Do you see what happened when I cut off the triangle and replaced it on the other side? Yes, it turned into a rectangle. Know we have proof and a good understanding that the area of a parallelogram is the same as the area of a rectangle which is Length*Breadth but as we are seeing it as a parallelogram it is Base*Height.

Triangle:- The area of a Triangle is easy to say when we know the area of a parallelogram.

If you observe the following figure, a triangle is arranged with its congruent one to form a parallelogram. So, the formula for the area of the parallelogram applies to the area of a triangle with a little change. Area of a triangle:1/2*Base*Height(as we need the area of only one triangle, not two!)