Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 1 - No. 17)
Which of the following must be true for the Pythagorean theorem to apply?
The triangle must be equilateral.
The triangle must have one angle equal to 90 degrees.
The triangle must have all angles equal to 60 degrees.
The triangle must be isosceles.
Explication
The Pythagorean theorem applies only to right-angled triangles.