MHB This is the formula for finding the area of a circle, where r is the radius.

[susanto3311]

hi guys..

i have a new challenge ...how to find are of circle..

like this ...

any body could help me, thanks so much..

susanto

 

[I like Serena]

hi guys..

i have a new challenge ...how to find are of circle..

like this ...

any body could help me, thanks so much..

susanto

Hey! ;)

It looks like a big half circle from which 2 smaller half circles are removed.
Let's start with those.
Can you tell what their radius's are? (Wondering)

 

[MarkFL]

Another approach would be to utilize the concept of similarity. The two smaller semi-circles have linear measures that are one-half that of the corresponding measures of the larger semi-circle, so we know their areas must each be one-fourth that of the larger. Since there are two of them, we then know the combined areas of the two smaller semicircles is one half that of the larger. So, find the area of the larger, and cut it in half (divide by two) and you will have the area in question. :D

 

[susanto3311]

Another approach would be to utilize the concept of similarity. The two smaller semi-circles have linear measures that are one-half that of the corresponding measures of the larger semi-circle, so we know their areas must each be one-fourth that of the larger. Since there are two of them, we then know the combined areas of the two smaller semicircles is one half that of the larger. So, find the area of the larger, and cut it in half (divide by two) and you will have the area in question. :D

hi Mark..

like this...

 

[MarkFL]

You want to find half of the area of the semi-circle...it appears you have found the area of the semi-circle...

edit: nevermind...it was unclear at first that you have divided by 2 twice...you should only use the equal sign to equate 2 quantities that are equal. :D

 

[susanto3311]

could you make more simple?...

 

[MarkFL]

More simple than finding half the area of a semi-circle? No. :D

 

[susanto3311]

how about...

= 308/2 = 154 cm2

it's true...??

 

[MarkFL]

I would write:

$$A=\frac{1}{2}\left(\frac{\pi}{2}(14\text{ cm})^2\right)=49\pi\text{ cm}^2\approx154\text{ cm}^2$$