![]() Right angle triangle :-A right-angled triangle or right triangle is formed when one of the triangle’s angles is 90 degrees.Acute Triangle: An acute-angled triangle or acute triangle is formed when all of the angles of a triangle are acute, that is, they measure less than 90 degrees.The following are the different sorts of triangles based on angles: There are various type of triangle are given below: Types of triangle based on angle:. TriangleĪ triangle is a closed 2-D polygon with 3 sides and a total angle of 180 degrees. ![]() In Euclidean geometry, a triangle is a two-dimensional form made up of three non-collinear points in a single plane. If EFG is a triangle, it is written as EFG, with E, F, and G as the triangle’s vertices. The angle sum property of a triangle is the name for this property. Interior angles sum equals 180 degrees is the feature of a triangle. (previous) .A triangle is a 3 -sided polygon with 3 edges and 3 vertices in geometry. 2021: Richard Earl and James Nicholson: The Concise Oxford Dictionary of Mathematics (6th ed.) .2014: Christopher Clapham and James Nicholson: The Concise Oxford Dictionary of Mathematics (5th ed.) .2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) .1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) .( The Elements: Book $\text$: Definition $19$) Rectilineal figures are those which are contained by straight lines, trilateral figures being those contained by three, quadrilateral those contained by four, and multi-lateral those contained by more than four straight lines. Note that \Delta is not to be used, as, although producing a symbol similar in shape, this is actually the uppercase Greek letter delta: $\Delta$ The $\LaTeX$ code to generate $\triangle ABC$ is written \triangle ABC. Results about triangles can be found here.The word trigon can occasionally be seen, but this is rare. Note that in order to emphasise the nature of the right angle in such a triangle, a small square is usually drawn inside it.Īn oblique triangle is a triangle in which none of the vertices are right angles.Īn acute triangle is a triangle in which all three of the vertices are acute angles.Īn obtuse triangle is a triangle in which one of the vertices is an obtuse angle. That is, a regular polygon with $3$ sides.Ī scalene triangle is a triangle in which all three sides are of different lengths.Ī right-angled triangle is a triangle in which one of the vertices is a right angle. $\angle A$ is adjacent to sides $b$ and $c$ Side $a$ is adjacent to $\angle B$ and $\angle C$ $\angle A$ is opposite side $a$ Side $a$ is opposite $\angle A$.Īn isosceles triangle is a triangle in which two sides are the same length.Īn equilateral triangle is a triangle in which all three sides are the same length: In order to emphasize that a particular vertex being referred to is in fact a vertex, the symbol $\angle$ is often placed by the letter corresponding to that vertex. The vertices of a triangle are conventionally labeled $A, B, C$ (or with other uppercase letters), and the sides with lowercase letters corresponding to the opposite vertex, as above. That is, the length of the altitude so defined. The height of a triangle is the length of a perpendicular from the apex to whichever side has been chosen as its base. In the above diagram, if $AC$ is taken to be the base of $\triangle ABC$, then $B$ is the apex. Having selected one side of a triangle to be the base, the opposite vertex to that base is called the apex. In the above diagram, it would be conventional for the side $AC$ to be identified as the base. The usual practice is that the triangle is drawn so that the base is made horizontal, and at the bottom. Thus, each vertex has an opposite side, and each side has an opposite vertex.įor a given triangle, one of the sides can be distinguished as being the base. The side of a triangle which is not one of the sides adjacent to a particular vertex is referred to as its opposite. Similarly, the two vertices of a triangle to which a particular side contributes are referred to as adjacent to that side. The two sides of a triangle which form a particular vertex are referred to as adjacent to that angle. A triangle is a polygon with exactly three sides.īecause it is a polygon, it follows that it also has three vertices and three angles.
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