Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 3 - No. 3)
What is a key characteristic of all right-angled triangles?
All sides are equal
One angle measures 90 degrees
All angles are acute
The sum of all the angles is 90 degrees
Explication
A right-angled triangle has one angle which measures 90 degrees.