How Do I Calculate the Area Covered by 4 Radio Transmitters in a 10 km Square?

[swither]

I have 4 radio transmitters, each in a different corner of a square with 10 km long sides. Each radio has a range of 10 km. I need to calculate the area where you are in range of all four transmitters. Unfortunately i have no idea how to do this. Can anyone help me?

//Swither

 

[Muzza]

Det marks nar Matte D borjar ta slut... ;)

See http://www.maths.lth.se/query/answers/q200210.html#20021014220806 for the solution.

 

[cyby]

! Is this an exam or something? :P Can't read Swedish myself...