The diameter of circle is 21 cm find its circumference with solution
Answers
Here is your answer
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The diameter of circle is 21 ..
Radius = 21/2
As we know that ,
The formula to find circumference = 2πr
The circumference of circle is 66 cm ..
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I HOPE IT WILL HELP YOU
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Assigning the names
Okay from now on:
Circumference will be known as C.
diameter will be known as d.
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Pi(the constant) derivation
Okay we learnt in class 8 the circumference of a circle is equal to 2πr
Now how did this come.We should know about its origin to believe that this formula is correct.
Now this is an experiment:
- Draw a circle of any radius.
- Measure the diameter.
- Measure its circumference with a string or something like that.
- You will notice that:-
C∝d
Circumference varies directly with diameter.So if circumference is to be increased just draw a circle having big diameter or radius.
Now we remove the ∝ sign with uh: a constant.
This constant never changes its value whatever the diameter whatever the circumference.
So : C=πd
We know d=2r obviously the diameter is twice the radius.
So : C=2πr.
We hence got this formula.
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Application of formula(just what students blindly do)
Which one is more easy :Ok the first one :
C=πd.
Wait here it is given that diameter is 21cm.
Oh just forgot to tell you the value of pi.
Pi=3.14 (this is very complex)
Pi=
Now this is easy.
C=πd.
Put the value of pi and diameter to get the solution.
cm
Come on we have to multiply 21 with 22 just get lost this is boring.
Wait we can diving 21 and 7 to get 3.
cm
cm.
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Answer
We found the circumference to be 66cm.
66cm
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Hope this helps you.
Just enjoy playing with mathematics. It is the most interesting subject ever.
Thanks for the question.
:-)