It is an angle that has a turn of less than 360 degrees which is a full turn.
Rotational Symmetry.
.less than
It is an acute angle in geometry because it's greater than 0 but less than 90 degrees
Assuming you are referring to a triangle. In Euclidean, or plane geometry, always to 180 degrees. In non-Euclidean geometry either more or less than 180 degrees.
Rotation Symmetry La Simetria de Rotation Symetrie de Rotation
Rotational Symmetry.
.less than
An angle less than 90 degrees.
It has rotational symmetry of order 2 or more.
It is an acute angle in geometry because it's greater than 0 but less than 90 degrees
Assuming you are referring to a triangle. In Euclidean, or plane geometry, always to 180 degrees. In non-Euclidean geometry either more or less than 180 degrees.
Rotation Symmetry La Simetria de Rotation Symetrie de Rotation
In hyperbolic geometry, triangles have angles that sum to less than 180 degrees, which contrasts with Euclidean geometry where the sum is exactly 180 degrees. This means that while hyperbolic triangles can still have angle measurements in degrees, the total of those angle measures will always be less than 180. Consequently, the concept of "degrees" is applicable, but the properties of the triangles differ significantly from those in Euclidean space.
Acute angles measure greater than 0 degrees and less than 90 degrees. Obtuse angles measure greater than 90 degrees and less than 180 degrees.
never In non-Euclidean geometry triangles can have angles that are more or less than 180 degrees.
There are 3 angle in any triangle. Iin plane geometry. collectively they will add up to 180 degrees. In non-Euclidean geometry the total will be greater or less than 180 degrees depending on which geometry is being used.
The proof is pretty simple, but hard to see without the pictures. SO here is a link to the proof with some pics. http://www.apronus.com/geometry/triangle.htm The answer depends on your geometry: In Euclidean geometry, the angle sum is 180 degrees, in Hyperbolic geometry it is less than 180 degrees, and in Elliptical geometry it is greater than 180 degrees.