[geometry] arc length - check my math

[TomTuff]

http://i254.photobucket.com/albums/hh115/tomtuff/Untitled.png

there's a group of problems on this diagram.
i'll list the problems, and if i have them, answers

#1: measure of arc EFG Answer: 160 degrees
#2: measure of arc EHG Answer: 200 degrees
#3: length of arc EFG Answer: approx 19.55
and now #4... you need to find the length of ehg. so what i did was find the circumference using c=7*pi, which came out to approx 21.99. i deducted 19.55 from 21.99, and that obviously came out wrong... i know that i should just do L=(200*pi*7)/180 to find that arc length, but still, this way should work, and it didnt.

EDIT: DUHHHHHHHHHHHHHHHHHHHH its C=14*pi... /facepalm

[i luffs yeww]

Diagram's not to scale. And EFG isn't 160 if FDG is 80 degrees. FG would be 160 if FDG is 80 degrees, wouldn't it?

[HyperSecret]

Why not use s=r(theta) [the equation for arc length]? theta is in radians.

160 degrees = 8pi/9
200 degrees = 10pi/9

EHG arc -> s= 7(10pi/9) = 70pi/9 = 24.42
EFG arc -> s= 7(8pi/9) = 56pi/9 = 19.54

Circumference of Circle = pi*diameter [not radius] = pi*14 = 43.98

EHG arc + EFG arc = 24.42 + 19.54 = 43.96

So these both agree with eachother.

[Nava2]

http://mathbin.net/equations/46705_0.png

[TomTuff]

Why not use s=r(theta) [the equation for arc length]? theta is in radians.

160 degrees = 8pi/9
200 degrees = 10pi/9

EHG arc -> s= 7(10pi/9) = 70pi/9 = 24.42
EFG arc -> s= 7(8pi/9) = 56pi/9 = 19.54

Circumference of Circle = pi*diameter [not radius] = pi*14 = 43.98

EHG arc + EFG arc = 24.42 + 19.54 = 43.96

So these both agree with eachother.


http://mathbin.net/equations/46705_0.png

perhaps because i'm a freshman in highschool just taking college prep geometry? ;)


Diagram's not to scale. And EFG isn't 160 if FDG is 80 degrees. FG would be 160 if FDG is 80 degrees, wouldn't it?

of course it's not to scale. it's a quick ms paint

and i forgot to mention that D is the center. And if an angle's vertex is the center of the circle, then the measure of the angle and the measure of the corresponding arc are the same.

[HyperSecret]

http://mathbin.net/equations/46705_0.png

Get that shit out of here... :D

I took CP Geometry too as a freshman...