Checking whether a triangle is right-angled

Use Pythagoras' theorem to check whether a triangle with given side lengths is right-angled.

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Learning objective overview

Master Teaching Guide coverage for this objective.

Current NZC (2007)
  • GM5-10
New NZC (2026)
  • NZC26-P4-MEA-MEA-P-Y10-10

Resources

Terminology

  • Pythagoras' theorem
  • converse of Pythagoras
  • right-angled triangle
  • hypotenuse
  • Pythagorean triple

Task goals

  • Apply the converse of Pythagoras' theorem to test whether $a^2+b^2=c^2$ holds for given side lengths.
  • Identify the longest side first, then compare the sum of squares of the two shorter sides against the square of the longest.
  • Distinguish between right-angled and non-right-angled triangles by checking the exact equality, not an approximation.
  • Recognise scaled Pythagorean triples (e.g. 6, 8, 10 as a scaled 3, 4, 5) and explain why they remain right-angled.

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Checking whether a triangle is right-angled

Checking whether a triangle is right-angled

Do

Using Pythagoras' theorem to: find the length of an unknown side in a right-angled triangle; check if a triangle has a right angle; calculate the distance between two points in the coordinate plane, yielding the distance formula d = √((x2 − x1)^2 + (y2 − y1)^2)

Statement▸
Year 10 · Measurement · Measuring
NZC26-P4-MEA-MEA-P-Y10-10

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