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HandWiki. Acute and Obtuse Triangles. Encyclopedia. Available online: https://encyclopedia.pub/entry/30937 (accessed on 20 October 2026).
HandWiki. Acute and Obtuse Triangles. Encyclopedia. Available at: https://encyclopedia.pub/entry/30937. Accessed October 20, 2026.
HandWiki. "Acute and Obtuse Triangles" Encyclopedia, https://encyclopedia.pub/entry/30937 (accessed October 20, 2026).
HandWiki. (2022, October 24). Acute and Obtuse Triangles. In Encyclopedia. https://encyclopedia.pub/entry/30937
HandWiki. "Acute and Obtuse Triangles." Encyclopedia. Web. 24 October, 2022.
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An acute triangle (or acute-angled triangle) is a triangle with three acute angles (less than 90°). 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. Acute and obtuse triangles are the two different types of oblique triangles — triangles that are not right triangles because they have no 90° angle.
angle
triangle
acute-angled
References
- Posamentier, Alfred S. and Lehmann, Ingmar. The Secrets of Triangles, Prometheus Books, 2012.
- Oxman, Victor, and Stupel, Moshe. "Why are the side lengths of the squares inscribed in a triangle so close to each other?" Forum Geometricorum 13, 2013, 113–115. http://forumgeom.fau.edu/FG2013volume13/FG201311index.html
- Wladimir G. Boskoff, Laurent¸iu Homentcovschi, and Bogdan D. Suceava, "Gossard’s Perspector and Projective Consequences", Forum Geometricorum, Volume 13 (2013), 169–184. [1]
- Inequalities proposed in “Crux Mathematicorum”, [2].
- Elam, Kimberly (2001). Geometry of Design. New York: Princeton Architectural Press. ISBN 1-56898-249-6.
- Mitchell, Douglas W., "The 2:3:4, 3:4:5, 4:5:6, and 3:5:7 triangles," Mathematical Gazette 92, July 2008.
- L. E. Dickson, History of the Theory of Numbers, vol.2, 181.
- Sierpiński, Wacław. Pythagorean Triangles, Dover Publ., 2003 (orig. 1962).
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