There are only two requirements for a right triangle. First, it has to be a shape with three sides---the "triangle" part. Second, one of the angles must be 90 degrees. That's it.

National 4 Trigonometric skills Calculating an angle in a right-angled triangle Trigonometry helps solve problems involving right-angled triangles using the sine, cosine or tangent ratios. SOH CAH ...

Labelling sides of a right-angled triangle for trigonometry When a question about right-angled triangles involves all three sides and no angles, Pythagoras’ theorem close Pythagoras ...

Part of that is the way it's taught. Students are taught the "unit circle" and its relationship to trigonometry, but many fail to make the leap on how crucial circles are for trig functions. With ...

The Pythagorean theorem provides an equation to calculate the longer side of a right triangle by summing the squares of the other two sides. It is often phrased as a2 + b2 = c2.