Fundamental trigonometry functions

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There are six trigonometric functions in Trigonometry: sine, cosine, tangent, cotangent, secant, and cosecant.

 

Sine

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  • Sine θ is the length of the leg opposite θ over the length of the hypotenuse:  

Cosine

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  • Cosine θ is the length of the leg adjacent to θ over the hypotenuse:  

Tangent

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  • Tangent of θ is the length of the leg on the opposite side of the triangle from the angle θ over the length of the leg of the triangle adjacent to the angle θ:  

These three can be memorized by use of the name of the princess "Soh Cah Toa," meaning:

  • "sine-opposite-hypotenuse
  • cosine-adjacent-hypotenuse
  • tangent-opposite-adjacent".

The remaining ratios are reciprocals of the previous ratios:

Cotangent

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  • Cotangent θ is the reciprocal of tangent θ:  

Secant

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  • Secant θ is the reciprocal of cosine θ:  

Cosecant

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  • Cosecant θ is the reciprocal of sine θ:  


Other considerations

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  • Since the hypotenuse of a right triangle is always the longest side,   and  
  • If we divide both sides of each of these inequalities by the positive number  , we get   and  
    or   and  

Table

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Angle values

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θ radians sinθ cosθ tanθ cotθ secθ cosecθ
0 0 1 0 undefined 1 undefined
30° π/6 1/2 2
45° π/4 1 1
60° π/3 1/2 2
90° π/2 1 0 undefined 0 undefined 1
180° π 0 -1 0 undefined -1 undefined
270° 3π/2 -1 0 undefined 0 undefined -1
360° 0 1 0 undefined 1 undefined

Quiz

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Other resources

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Basic Trigonometry (Youtube)
Basic Trigonometry II (Youtube)