In a rectangle, the opposite sides are equal. The diagonal connects the opposite ends of the rectangle. This means that a right angle triangle can be formed as shown in the diagram below
Looking at the door frame above, we would confirm if it is actually a rectangle by applying pythagoras theorem which is expressed as
Hypotenuse^2 = opposite side^2 + adjacent side^2
It becomes
86^ = 80^2 + 32^2
7396 = 6400 + 1024
7396 is not equal to 7424
We can see that pythagoras theorem was not obeyed. Therefore,
The door frame is not a rectangle
