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Intuition behind Pythagoras Theorem

  • Last Updated : 01 Jul, 2021

The Pythagoras Theorem states that in a right angled triangle, ‘a’ being the base, ‘b’ being the height and ‘c’ being the hypotenuse of  that triangle, then a2+b2=c2

Below is an illustration of this –

Example –

1. if the base of a right angled triangle is 3, the height is 4,then what is the length of its hypotenuse?
Solution –  given, a=3, b=4 ,c=?
          Using Pythagoras theorem, 
          √(9+16) =c

2. if the hypotenuse of a right angled triangle is 13, the height is 5,then what is the length of its base?
Solution –
given, a=?, b=5 ,c=13    
Using Pythagoras theorem,          

Intuition behind Pythagoras Theorem :
Let’s prove this theorem using the figures. 
Draw squares corresponding to each side of the triangle as follows –

If we look at the figure closely, we could reframe the pythagoras theorem as follows-
The area of 2 squares is equal to the third square.
ie- a2 is the area of the 1st square
     b2 is the area of the 2nd square
     c2 is the area of the 3rd square

thus, a2+b2=c2
Another proof of pythagoras theorem can be shown by rearranging the triangles to form 2 squares as follows

If we compare the two squares, we can find that both the squares have a+b side length, thus having the same area.
In each square, four right-angled triangles are used (realigned in a different way though)
So, we can conclude that

area(1st square) =a rea(2nd square)
c2 + 4* (area of a right angled triangle)=  a2+b2+4* (area of a right angled triangle)
c2=a2+b2  [cancelling the common terms from both sides]

Thus, pythagoras theorem is proved.

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