Current Affairs 7th Class

Category : 7th Class

Perimeter and Area

• Perimeter is the distance around a closed figure.
• Area is the part of plane occupied by the closed figure.

            (a) Perimeter of a square= 4\[\times \]side units

            (b) Perimeter of a rectangle = 2\[\times \](length + breadth) units

            (c) Area of a square = side \[\times \] side sq. units

            (d) Area of a rectangle = length \[\times \] breadth sq. units

• Area of a parallelogram = base \[\times \] height sq. units
• Area of a triangle =\[\frac{1}{2}\](area of the parallelogram generated from it)

            = \[\frac{1}{2}\] \[\times \]base \[\times \] height sq. units

• Area of a trapezium =\[\frac{1}{2}\](a + b) h sq. units, where \['a'\]and \['b'\] are lengths of parallel sides and 'h' is the height.

• A circle is a closed curve in a plane drawn in such a way that every point on it is at a constant distance (r units) from a fixed point 0 inside it.

            The fixed point 0 is called the centre of the circle and the constant distance r is called the radius of the circle.

• Circumference of a Circle: The perimeter of a circle is called its circumference.
• Circumference =\[2\pi r\] =\[\pi \]d, where r = radius and d = diameter.

            Here \[\pi \](Pi) is a constant, equal to 3.14 approximately.

• Area of a Circle: Area of a circle with radius r units is equal to \[\pi {{r}^{2}}\] sq units.
• Area of a Ring:

• The region enclosed between two concentric circles of different radii is called a ring.

            Area of path formed between two concentric circular regions \[=\left( \pi {{R}^{2}}-\pi {{r}^{2}} \right)\] sq. units

            \[=\pi \left( {{R}^{2}}-{{r}^{2}} \right)\]square units

            \[=\pi \left( R+r \right)\left( R-r \right)\]square units