It has to be 90 degrees to be a right angle.
In Euclidean geometry, a triangle must be one of these: acute, obtuse, or right. Maybe there is a non-Euclideangeometry for which some obtuse triangles can contain a right angle, but it doesn't happen in Euclidean geometry.
An equilateral triangle on on of the arms of the right angle.
Because the phrase 'right angle' indicates 90 degrees whereas there is no such angle as a 'left angle'
A right-angle triangle must have one corner of 90 degrees.
It has to be 90 degrees to be a right angle.
In Euclidean geometry, a triangle must be one of these: acute, obtuse, or right. Maybe there is a non-Euclideangeometry for which some obtuse triangles can contain a right angle, but it doesn't happen in Euclidean geometry.
It could be a right angle or a reflex angle
That it must be a right angle triangle because the 3rd angle must be 90 degrees
An equilateral triangle on on of the arms of the right angle.
triangle
Because the phrase 'right angle' indicates 90 degrees whereas there is no such angle as a 'left angle'
A right angle triangle must have a 90 degree angle and two acute angles.
Acute triangles. They can have three angles, all less than 90 degrees (total is 180 degrees).Shapes with more than three sides must have angles of 90 degrees or more because the total of their angles must be 360 degrees (quadrilaterals) or more.
A right-angle triangle must have one corner of 90 degrees.
One angle must be 90o, which is the right angle. The sum of the other two angles must equal 90o.
It can be any length; a right angle triangle just needs to include a right angle somewhere. But length has nothing to do with whether it is a right angle or not.