Stage: 5 Challenge Level: 
Prove that for every right angled triangle which has sides with integer lengths:
- the area of the triangle is even and
- the length of one of the sides is divisible by 5.
Pythagoras' theorem. Pythagorean triples. Factors and multiples. Index notation/Indices. Mathematical reasoning & proof. Long problems. Quadratic equations. Divisibility. Circles. Modulus arithmetic.
Published May 1998.
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