- An acute triangle (or acute-angled triangle) is a triangle with three acute angles (less than 90°).
- Wikipedia redirects to a page that combines information for acute and obtuse triangles.
- Obtuse triangle (Wikipedia)
An obtuse triangle (or obtuse-angled triangle) is a triangle with one obtuse angle (greater than 90°) and two acute angles. Since a triangle’s angles must sum to 180° in Euclidean geometry, no Euclidean triangle can have more than one obtuse angle.
- Right triangle (Wikipedia)
A right triangle or right-angled triangle, sometimes called an orthogonal triangle or rectangular triangle, is a triangle in which two sides are perpendicular forming a right angle (1⁄4 turn or 90 degrees).
