And further of the trilateral figures: a right-angled triangle is that having a right angle, an obtuse-angled (triangle) that having an obtuse angle, and an acute-angled (triangle) that having three acute angles.
A triangle with: * a right angle is called right-angled (or right), * one obtuse angle is called obtuse-angled (or obtuse), * three acute angles is called acute-angled (or acute).
A right triangle:
An acute triangle:
A obtuse triangle:
Corollaries: 1 2
Definitions: 3 4
Lemmas: 5
Proofs: 6 7 8 9 10 11 12 13 14
Propositions: 15 16 17 18
Solutions: 19 20
Topics: 21