Math Is Fun Forum

stellina91

Member

Registered: 2008-04-15

Posts: 12

Geometry Question

Find the angles x and y in the diagram.  Give reasons for each step in your arguments. 

I don't know where to start!  Can someone please help me.

Thank you.

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Re: Geometry Question

Total degrees in a circle is 360. So if that part is 120 and the total is 360 then:

y + 120 = 360
y = 240 degrees

Is the AB line parallel to the CD line? You dont specify it?

I will assume it is.

I dont know how to give a logical geometric proof but this is my logic:

Suppose the AB line keeps going. This angle is 60 degrees because the half circle formed by the line is total 180. Since AB and CD are parallel (?) then the other angle is also 60 degrees and x is also 60 degrees. I do not recall the theorem names but each of this steps I did was because of certain theorems having to do with parallel lines in geometry.

Hope this helps.

Last edited by LuisRodg (2008-04-15 14:06:43)

stellina91

Member

Registered: 2008-04-15

Posts: 12

Re: Geometry Question

Thank you very much for your help.  It's greatly appreciated, sorry I must have forgotton to put the arrow on the AB line.

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Re: Geometry Question

Did you understand all I did? As I said, every step I took is backed up by geometrical theorems which I dont recall their names. I suppose you do?

stellina91

Member

Registered: 2008-04-15

Posts: 12

Re: Geometry Question

Yeah I do, thanks a lo but I'm not sure which reasons to give.

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

Re: Geometry Question

"corresponding angles"
"alternate interior angles"
See this link and scroll down for more of them.
http://www.mathleague.com/help/geometry/angles.htm#verticalangles

---

igloo myrtilles fourmis

LuisRodg

Real Member

Registered: 2007-10-23

Posts: 322

Re: Geometry Question

Thanks Franklin.