# Math Help - Geometry problem

1. ## Geometry problem

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

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

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

I'm not sure how to solve it because I got confused by the teacher.
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. there seems to be some useful theorem that i'm forgetting at the moment

3. $\displaystyle\widehat{DAE}=\frac{1}{2}(arc(DE)-arc(GF))$
$arc(GF)=180-60-90=30$
Then $\displaystyle\widehat{DAE}=\frac{1}{2}(60-30)=15$

4. 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

5. Thanks for the help!