Circumference and Area of A Circle

[susanto3311]

hello expert...

How to find the circumference of a circle and area of a circle quickly?
it's possible using method like ratio or series like pythagoras theory (3,4,5).
or another way?

somebody could help me out?

cheers...
susanto3311

 

[MarkFL]

What do you know about the circle?

 

[SuperSonic4]

You can find both using the radius (or diameter) of the circle. The main way to find them is also the quickest way

 

[susanto3311]

hi guys...

i want to easy find area & circumference of circle to multiple choice exam with "tactics & logic" approach, again like triagle phytagoras concept just know 3,4 the last result must be 5..

 

[SuperSonic4]

I'm still not 100% sure what you're asking. I get the impression you want to know a way of finding the area of a circle without having to work it out in the same way that if you know two sides of a right angled triangle are 3 and 4 then the third must be 5.

If so then the only real shortcut is to learn the results. I would also use exact answers (left in terms of \(\displaystyle \pi\)) as it's both easier to work out and correct (not an approximation).

In multiple choice it may be worth saying \(\displaystyle \pi \approx 3\)

---

If you're given the diameter instead of the radius then you can use these formulae:

\(\displaystyle C = \pi d\) and \(\displaystyle A = \frac{\pi}{4} d^2 \) where \(\displaystyle d\) is the diameter.

Just remember not to use that approximation too much...
[youtube]V98soOyQWKY[/youtube]

 

[susanto3311]

hello guys...

I found the nearest value of area of the circle with a simple trick using vedic maths..

please, read this link http://vedicmathstricks.yolasite.com/

how do make formula for find the nearest value of circumference of the circle?

any ideas?

thanks...

 

[MarkFL]

It appears to me what is being done there is to use 22/7 as an approximation for $\pi$ (I recall using this approximation in primary school). If you require more decimal places, then you can use 355/113.

 

[susanto3311]

hello guys...

I found the nearest value of area of the circle with a simple trick using vedic maths..

please, read this link http://vedicmathstricks.yolasite.com/

how do make formula for find the nearest value of circumference of the circle?

any ideas?

thanks...

using vedic method, how to find easy radius? i mean simple calculation..

 

[MarkFL]

If we are given the area $A$ of a circle, or the circumference $C$, then using the rational approximation:

\(\displaystyle \pi\approx\frac{22}{7}\)

then we find:

\(\displaystyle A\approx\frac{22}{7}r^2\implies r\approx\sqrt{\frac{7A}{22}}\)

\(\displaystyle C\approx2\cdot\frac{22}{7}r\implies r\approx\frac{7C}{44}\)