Hyperbolic geometry or hypercycle, then the triangle has no circumscribed circle. As in spherical and elliptical geometry, in hyperbolic geometry if two triangles are similar, they must be congruent. A special polygon in hyperbolic geometry is the regular apeirogon, a uniform polygon with an infinite number of sides. In Euclidean geometry, the only way to construct such a polygon is to make the side lengths tend to zero and the apeirogon is indistinguishable from a circle, or make the interior angles tend to 180 degrees and the apeirogon approaches a straight line. However, in hyperbolic geometry, a regular apeirogon has sides of
Protractor traditionally been one-sided. This is thought to be because early manufacturing methods set the tone of future production. Unfortunately, the two number scales on a one-sided protractor often confuse learners when first learning to measure and draw angles. However, in 2009, Jake Adamson, a maths teacher working at Musselburgh Grammar School invented and patented the first two sided protractor trademarked "The Angler". This was a double sided protractor with one scale on each side, avoiding the confusion of having two scales together and enabling easier measuring and drawing of angles. "The Angler" protractor has been widely adopted by schools in