congruent

Small question: does congruent mean the angles of a shape are the same as another or is it that one shape is the same as another or is it that one shape is proportionally the same as another?

Also for C2 isn't half of r 3? Then why is it 6?

And why do we divide by 2 if it's a quadrilateral?

@TSSGraviser Congruent means that two shapes have the same angles and the same side lengths, so that they could be stacked on top of each other like postit notes, to fit exactly.