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The Man and the Theorem
A Greek coin showing Pythagoras
• Pythagoras was born on the Greek island of Samos in c. 475 BC
• He travelled to Egypt to learn mathematics and astronomy.
• Founded a school in Samos called the Semicircle.
• He founded a secret sect in Croton (Southern Italy)
A Greek stamp showing Pythagoras
• Women were allowed to join this sect
• The members were vegetarians but beans were excluded from their diet
• Clay tablets (1800 BC and 1650 BC) show that the Babylonians already knew about the Theorem
• The Egyptians could have used it to construct right angles when they build the pyramids
A Babylonian tablet
• Pythagoras was probably the first to prove the theorem.
• He is reputed to have proved the theorem while hiding in a cave from the tyrant Polycrates. The cave of
Pythagoras at the foot of Mount Kerki, in
Samos. • Legend has it that he sacrificed
an ox to thank the gods!
• The theorem states that in any right angled triangle ….
b c
a
The square of the hypotenuse is equal to the sum of the squares of the other sides.
b c
a
c2 = a2 + b2
• There are nearly 400 proofs of the theorem!
James A. Garfield 30th President of the
United States
• Among them is a proof by an American president.
• Area of red triangle: ½ a b
b
a
b
a
c
c• Area of blue triangle: ½ a b
• Area of green triangle: ½ c 2
• Area of trapezium:
½ (a + b)2
b
a
b
a
c
c
• Therefore
½ (a + b)2 = ½ a b + ½ a b + ½ c 2
(a + b)2 = 2a b + c 2
a 2 + b 2 + 2a b = 2a b + c 2
a 2 + b 2 = c 2
Area of square = c 2
Area of each triangle = ½ ab
Area of central square= ½ (a b) 2
Area of square = c 2
= 4x ½ ab + (a b)2
= 2ab + a 2 2ab + b 2
c 2 = a 2 + b 2
a
b c
Consider a cuboid of length a, width b and height c.
a
b c
We want to find the distance d from one corner to the other
d
x
x2 = a2 + b2
d 2 = x2 + c2 hence d 2 = a2 + b2 + c2
• There are cases when the lengths of the sides of a right-angled triangle have integral values
3
4
5• The 3, 4, 5 right-angled triangle
is such a case
The numbers 3, 4 and 5 are said to form a
Pythagorean Triple 52 = 32 + 42
• There are an infinite number of Pythagorean triples
• Here are two more examples …
5
12
13
257
24
finis