Right triangle and trigonometric functions
Right triangle and trigonometric functions
A right triangle (Fig. 1) is a triangle that has one of its angles equal with 90º. In this case γ=90°. AB, the triangle’s side opposite to the 90° angle, is called the hypotenuse; BC and AC, the triangle’s sides adjacent with the 90° angle, are called legs.
α, β and γ are the triangle’s angles and their sum is equal with 180°.
(α + β + γ = 180°).
γ = 90° therefore α + β =90°.
Trigonometric functions (circular functions) are functions of the angle.
In below table are shown the trigonometric functions, functions of the angle .

Applying Pythagoras Theorem to the triangle in Fig 1 we have:
In other words, we can say that in a right triangle the hypotenuse’s squared value is equal with the sum of the legs’ squared values.
By dividing both sides of the equality in [1] by we get:
by replacing with and with we get:
[3]
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