Special right triangle is 90°, leaving the remaining angle to be 30°. Right triangles whose sides are of integer lengths, with the sides collectively known as Pythagorean triples, possess angles that cannot all be rational numbers of degrees. (This follows from Niven's theorem.) They are most useful in that they may be easily remembered and any multiple of the sides produces the same relationship. Using Euclid's formula for generating Pythagorean triples, the sides must be in the ratio where "m" and "n" are any positive integers such that . There are several Pythagorean triples which are well-known, including those with sides in the
Perceived visual angle specifies the amount by which one should rotate one's eye to quickly look from one seen point to another eye tracking, saccade, observers in other experiments shifted their gaze from one object endpoint to the other, and the angle the eye rotated through was measured as "θ′" for that object (Yarbus (1967). It is important to understand how "θ′" differs from "S′". Consider an example illustrated by the sketch at the right. Suppose one is looking through a window at a house 240 feet away, so it subtends a visual angle of about 7 degrees. The window opening is 10