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if the 3 sides of one triangle is equal to the 3 sides of the other triangle then both
these triangles are congruent. we will try and prove this with a piece of paper. first
fold the paper in the middle and this middle line or the fold line will be called as PQ.
on this fold line mark a point C and then open the paper so that the mid line is exposed.
now on left side fold a crease and mark a line whose two ends would be A and B. now
once again fold the paper on its mid line PQ and with the point of a divider poke holes
on A and B so that the points A and B are marked on the other layer of paper too. now
fold C to A and crease well. similarly crease C to B to make the triangle ABC. mark the
triangle ABC with a pen. now open the paper and mark A' and B' on the two holes. now angle
C will be equal to its opposite angle on the right side. now fold the paper along A'B'
and cut off the extra piece of paper. now fold A' to C and cut along A' to C. similarly
crease B'C and also cut along this line. now triangle on the right side CA'B' can be superimposed
on triangle ABC and you will see that right hand triangle is exactly on the left hand
triangle with all the sides equal. so triangle ABC is congruent to triangle A'B'C.