Explanation:
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There are two "special" right triangles:
isosceles 45°-45°-90° triangle with sides in the ratios 1 : 1 : √2
30°-60°-90° triangle with sides in the ratios 1 : √3 : 2
These side lengths give rise to the trigonometric ratios shown below for angles with 30°, 45°, or 60° as reference angles.
