Answer:
It is because not all sides of a rectangle are equal in length; unlike a square.
Step-by-step explanation:
Let's start by drawing the first diagonal.
You know already how a rectangle looks. It has 4 sides and 2 sets of parallel sides. Each pair of parallel sides has the same length.
A diagonal is a line crossing from one edge of a four-sided shape to the opposite edge; such that it divides the shape into two equal halves.
Now place your rectangle horizontally. Let the two longer sides be on the horizon while the two shorter sides go vertical.
We draw the first diagonal from the edge on the top right to the opposite edge (down left). This will divide the shape into two equal halves and each half will be a triangle; a congruent one at that.
When you fold this rectangle along its diagonal, the two triangles will not overlap! The resulting shape will be like two triangular mountains lying side by side. You can use a paper (cut in the shape of a rectangle) for this experiment.
Why does this happen, instead of the two triangles covering each other (overlapping)?
This happens because a rectangle doesn't have 4 equal sides. Check out a square and you'll see that both triangles will overlap after a diagonal is drawn across the square.
Draw the second diagonal of the rectangle (from up-left to down-right) and the same thing is observed.
