Proving Cyclic Quadrilateral: Opposite Angles Sum 180°

[physics kiddy]

Homework Statement

I have got a question that might be easy for you. But, not for me.

I have attached a pic. Please tell me if the quadrilateral inside the circle is a cyclic quadrilateral or not. If it is, then please explain how to prove that it's opposite angles sum up to 180 degrees

Homework Equations

I believe it won't require any equation.

The Attempt at a Solution

No idea !

 

[micromass]

What is the definition of a cyclic quadrilateral??

 

[Joffan]

As for proof, this might help: http://en.wikipedia.org/wiki/Inscribed_angle