Mensuration (Perimeter & Area)
Category : 7th Class
MENSURATION (Perimeter and Area)
FUNDAMENTALS
(a) Perimeter of a square \[=4\times \] side.
Elementary question-1: Find perimeter of a square kabaddi field each of whose side is 20 metres
Ans. Perimeter \[=4\times 20=80\,m\]
(b) Perimeter of a rectangle \[=2\times \] (length + breadth) units.
(c) Area of a square = (side \[\times \] side).
(d) Area of a rectangle = length \[\times \] breadth.
Elementary Question-2: Find perimeter and area of a football field whose length and breadth are 40 metres and 70 metres respectively.
Ans. Perimeter \[=2\times (40+70)=220\,m\]
Area \[=40\times 70=2800\text{ }Sq.\text{ }m.\]
(e) Area of a parallelogram = base \[\times \] height sq. units.
(f) Area of a triangle \[=\frac{1}{2}\] (Area of the parallelogram generated from it)
\[=\frac{1}{2}\times \]base \[\times \] height sq. units
The fixed point, O is called the centre of the circle and the constant distance r is called the radius of the circle. Here, we can introduce the idea of "locus". Circle is locus of points P whose distance form a fixed point '0' is constant. 'O' is called centre and OP is called radius of the circle.
The region enclosed between two concentric circle of different radii is called a ring. Area of path formed between two concentric circular regions \[={{(\pi {{R}^{2}}-\pi r)}^{2}}\,sq.\] sq. units.
\[=\pi ({{R}^{2}}-{{r}^{2}})\] square units
\[=(R+r)\,\,(R-r)\] square units
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