In a right triangle, considering the measure an acute angle call:
sine (sinus) = the cathetus opposite / hypotenuse Sine (sinus), cosine, tangent and cotangent are called trigonometric functions and is denoted by sin, cos, tan, and ctg. 
In the above triangle, ABC, we have

Given a right triangle ABC with rectangle A, the following are true relationships:
basic trigonometry formula

We do not here only the most popular values of trigonometric functions (table below):
u  0^{0}  30^{0}  45^{0}  60^{0}  90^{0} 
sin u  0  1  
cos u  1  0  
tg u  0  1  ∞  
ctg u  ∞  1  0 
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