As shown in the figure, point C is a point on line AB, D and E are the midpoint of AC and BC respectively, then de = 0___ AB.

As shown in the figure, point C is a point on line AB, D and E are the midpoint of AC and BC respectively, then de = 0___ AB.

As shown in the figure, D and E are the midpoint of AC and BC respectively, CD + CE = AD + be, de = 12ab