mitre

If I draw a four sided box, how can I split it into four parts? https://cad.onshape.com/documents/519a41adbb034d51bae1ef5f/w/5cdc28e704584357975c1ef2/e/80c892160dd749da88240570 I know I could just draw a sketch with mitres then extrude each side as a new part. But say for some reason I decided to make life difficult for…