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Mathematics 7 Online
OpenStudy (anonymous):

Can someone please explain to me how this is wrong????

OpenStudy (anonymous):

OpenStudy (jdoe0001):

|dw:1404946673527:dw| \(\bf \textit{area of a segment of a circle}=\cfrac{{\color{brown}{ r}}^2}{2}\left(\cfrac{{\color{brown}{ \theta}}r}{180}-sin({\color{brown}{ \theta}})\right)\)

OpenStudy (anonymous):

I found the area of the hole circle which is 153.93804 then i multiplied that by 35 which is 5387.831 then i did 5387.831/360 which equals 14.96619?

OpenStudy (anonymous):

Then i rounded to the nearest hole number which is 15

OpenStudy (jdoe0001):

|dw:1404946978668:dw|

OpenStudy (jdoe0001):

you're correct, is 14.9 which rounds to 15, yes, for the "sector" of the circle

OpenStudy (anonymous):

Ok when i plug the numbers into the equation up there i get .787535? is that right?

OpenStudy (jdoe0001):

hmmm wait a sec... I missed something there

OpenStudy (jdoe0001):

hmmm no .... shoot.. just have a typol lemme fix that quick

OpenStudy (jdoe0001):

\(\bf \textit{area of a segment of a circle}=\cfrac{{\color{brown}{ r}}^2}{2}\left(\cfrac{{\color{brown}{ \theta}}\pi}{180}-sin({\color{brown}{ \theta}})\right) \\ \quad \\ \implies \cfrac{{\color{brown}{ 7}}^2}{2}\left(\cfrac{{\color{brown}{ 35^o}}\cdot \pi}{180}-sin({\color{brown}{ 35^o}})\right)\)

OpenStudy (phi):

as jdoe shows, the *segment* is the part of the sector cut off by a chord

OpenStudy (phi):

Another "formula" is to subtract off the area of the isosceles triangle with sides 7 and vertex angle 35º (a bit complicated, because you must use trig, but it's easier to remember, than the formula posted up above)

OpenStudy (anonymous):

Ok thanks

OpenStudy (jdoe0001):

yw

OpenStudy (phi):

the triangle has an altitude of 7 cos(35/2) and base 2*7*sin(35/2) and area 7*7*sin(35/2)*cos(35/2) and if you know sin(2x) = 2 sin(x)cos(x) ½*7*7*sin(35)

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