Notes on Perimeter | Grade 7 > Compulsory Maths > Perimeter, Area and Volume | KULLABS.COM

Perimeter

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Perimeter of Plane Figure

All the Triangle , Circle , Square, and Rectangle are plan figure . The total length of the boundary lines of plan figure is called its perimeter.Perimeter of Triangles :

Perimeter of Triangles :

The sum of the length of its three sides is known as a perimeter of triangles . Therefore,

\(\therefore\) Perimeter of \(\triangle DEF\) =DE + EF+ FD = a+b+c

The half of its perimeter is known as semi -perimeter of triangle . It is denoted by the letter 's'.

\(\therefore\) Semi -perimeter of \(\triangle\)DEF= \(\frac{a+b+c}{2}\)

Perimeter of Rectangles :

The opposite sides of rectangle are always equal . So , the lengths = EF=GH=l

the breadths =FH=EG=b

The perimeter of the rectangles EFGH =EF+FG+GH+HG

=l+b+l+b=2l+2b

=2(l+b)

\(\therefore\)Perimeter of rectangle = 2(l+b)

In the case of Square , its perimeter =2(l+l)

=2x2l=4l

Perimeter of circles :

At first draw three circles with radii 2cm , 3cm, and 4cm, and place the pieces of strings along the circumference of each separately .

Then start measuring the length of each string separately with the help of scale . Then, find the ratios of the length of the circumference of each circle to its diameter . Now , you all will find the ratio \(\frac{circumference}{diameter}\) is almost the same for every circle. The constant ratio is represented by Greek letter 'π' (pie). So , the circumference of circle iscand its diameter bed,

Now , \(\frac{circumfernce }{diameter})=π

or, \(\frac{c}{d})=π

or, c=πd

Diameter of circle (d) =2xradius (r).

So, circumference or the perimeter of circle (c) =2πr

The perimeter of circle =πd or2πr



  • All the Triangle , Circle , Square, and Rectangle are plan figure . The total length of the boundary lines of plan figure is called its perimeter. 
  • The sum of the length of its three sides is known as a perimeter of triangles .
  • The opposite sides of a rectangle are always equal .
.

Very Short Questions

Solution:

Here,
the length of the field (l) = 25 m
the perimeter of the field = 86 m
Now, 
the perimeter of the rectangular field = 86 m
or, 2(l + b) = 86 m
or, 25 + b = \(\frac{86}{2}\) m
or, 25 + b = 43 m
or, b = (43 - 25) m
or, b = 18 m
∴ the required breadth of the field is 18 m


Solution:

Here,
the radius of the circular ground (r) = 35m
its perimeter = 2πr
= 2 × \(\frac{22}{7}\) × 35 m
= 2 × 22 × 5
= 220 m
∴ The required length of wire = 4 × 220m
= 880 m
Again,
the required cost of fencing = 880 × Rs 10
= Rs 8800

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  • What is the formula of  perimeter of rectangle?

    l + b
    2 l + b
    2(l + b)
    4 l 
  • What is the formula of perimeter of a circle?

    πr2
    πr
    (πr)2
    2πr
  • What is the formula of a semi-perimeter of a triangle?

    a + b + c
    (frac{a + b + c}{3})
    (frac{a + b - c}{2})
    (frac{a + b + c}{2})
  • If the perimeter of a rectangular field of length 25m is 86m, what will be its breadth.

    21m
    18m
    15m
    13m
  • If the perimeter of a circular ground is 352m, what will be its radius?

    73m
    56m
    24m
    43m
  • If the circumference of a circular field is 132m then what will be its diameter.

    19m
    12m
    42m
    38m
  • In the equilateral triangle whose one of the side is 4.5 cm them what will be its perimeter?

    18.3 CM
    16.2 cm
    11.2 cm
    12.4 cm
  • Find the semi-perimeter of a triangular park whose lengths are 15m, 20.5m and 17.5m.

    21.3 m
    26.5 m
    25.4 m
    23.6 m
  • The Semi-perimeter of a triangle is denoted by ______.

    s
    t
    p
    s-p
  • The value of "π" is ______ .

    (frac{22}{7})
    (frac{2.2}{7})
    (frac{7}{22})
    22
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