Firstly draw two circles with center O and O′ such that they intersect at A and B.
Draw a line PQ parallel to OO′.
In the circle with center O, we have:
OP and OB are the radii of the circle. PB is the chord with OM as its perpendicular bisector.
i.e. BM=MP....(1)
In the circle with center O′, we have:
O′B and O′Q are the radii of the circle. BQ is the chord with O′N as its perpendicular bisector.
i.e. BN=NQ....(1)BM=MP....(1)
From (1) and (2), we have:
BM+BN=MP+NQ⇒(BM+BN)+(BM+BN)=(BM+BN)+(MP+NQ)⇒2(BM+BN)=(BM+BN)+(MP+NQ)⇒2(OO′)=(BM+MP)+(BN+NQ)⇒2(OO′)=BP+BQ⇒2OO′=PQ
Hence, proved.