# Geometry problem

• Sep 13th 2007, 04:56 AM
jenna14
Geometry problem
In circle C - I need to find AC, AB, FE and angle DAE.

http://img529.imageshack.us/img529/2...problemfx4.jpg

I'm not sure how to solve it because I got confused by the teacher. :rolleyes:
• Sep 13th 2007, 08:06 AM
Jhevon
Quote:

Originally Posted by jenna14
In circle C - I need to find AC, AB, FE and angle DAE.

http://img529.imageshack.us/img529/2...problemfx4.jpg

I'm not sure how to solve it because I got confused by the teacher. :rolleyes:

is C the center? (so the radius would be 10)?

if so, AC = AG + GC, where GC is the radius

we can find AB using Pythagoras' theorem

to find FE, you can draw a line from F to C and from E to C. note that you will form an isosceles triangle, with the angle at the center = 90 degrees. i think you can take it from there

to find angle DAE ... i have to think about some more:rolleyes:. there seems to be some useful theorem that i'm forgetting at the moment
• Sep 13th 2007, 09:35 AM
red_dog
$\displaystyle\widehat{DAE}=\frac{1}{2}(arc(DE)-arc(GF))$
$arc(GF)=180-60-90=30$
Then $\displaystyle\widehat{DAE}=\frac{1}{2}(60-30)=15$
• Sep 13th 2007, 09:46 AM
Jhevon
Quote:

Originally Posted by red_dog
$\displaystyle\widehat{DAE}=\frac{1}{2}(arc(DE)-arc(GF))$
$arc(GF)=180-60-90=30$
Then $\displaystyle\widehat{DAE}=\frac{1}{2}(60-30)=15$

that's the theorem i was forgetting. i thought it only worked for tangents though. that is, AE and AD had to be tangents, oh well
• Sep 13th 2007, 11:35 AM
jenna14
Thanks for the help!