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In
another article we looked at Pythagoras' theorem about
right-angle triangles. It says that if you square the longest side
(called hypotenuse) it will equal the squares of the other two
sides added together.
When drawing one of these it doesn't matter what length you make
the first side, the theorem will always work. For example, if I
made the bottom side 6 cm and the small side 2 cm, I can work out
the longest side by...
(6 x 6) + (2 x 2) = (longest side x longest side)
36 + 4 = 40
so 40 = (longest side x longest
side)
Now we have to find the square root of 40. A calculator is helpful
because the answer is somewhere in between 6.32 cm and 6.33
cm.
So most sets of three side-lengths will have a fraction in them.
You have to work quite hard to find lengths for each side that are
all whole numbers. These sets of three whole numbers are called
Pythagorean Triples, like 3, 4, 5. ($3^{2} + 4^{2} = 5 ^{2}$; that
is 9 + 16 = 25) Another Pythagorean Triple is
5, 12, 13 . Another is
7, 24, 25 . What do you notice about
these sets of numbers?
Now here's a bit of fun from Allan White (Australia):
Liethagoras (say "Lie-thag-or-us" - get it?!) was a long
distant cousin of Pythagoras. He was very jealous of Pythagoras,
because his theorem had given number triples that gave right
triangles such as 3, 4, 5 or 5, 12, 13 or 7, 24, 25. So he thought,
"If only I could come up with a theorem that was simpler than
Pythagoras, then I too would be famous". So he thought and he
thought until he had a wonderful thought and he rushed off to tell
the mathematicians.
His theorem was: In any right
triangle the square of the smallest side equals the sum of the
other sides.
For example:
In the 3, 4, 5 Triangle 3 x 3 = 4 +
5
In the 5, 12, 13 triangle 5 x 5 = 12 +
13
Does it work for the 7, 24, 25
triangle?
Instead of becoming famous, the
mathematicians just laughed at him. Why did they laugh at
him?
Let's investigate:
1. Can you find a number triple that obeys Liethagoras' theorem but
doesn't obey Pythagoras' theorem and so doesn't give a right
triangle?
2. Can you find a number triple that
obeys Pythagoras' theorem but doesn't obey Liethagoras'
theorem?
3. Liethagoras' theorem only works on
Pythagorean triples that ...
That's something for you to work on.