In Figure, l m and M is the mid-point of a line segment AB. Show that M is also the mid-point of any line segment CD, having its endpoints on l and m, respectively.
Given :
M is the mid-point of AB then AM = MB
To show:- M is the mid-point of CD.
Proof:-
Then, In ACM and DMB
ACM = BDM (Alternate interior angles are equal)
AMC = DMB (vertically opposite angles are equal)
AM = MB (given)
then by AAS criterion of congruence
ACM BDM
Then DM = CM (CPCT)
and CD = DM + MC = 2 DM
DM = CM = CD
Then M is also the mid-point of CD.
Hence proved.