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Based on the three basic trigonometric ratios \sin, \cos and \tan we will define its reciprocals.
Reciprocal Ratios:
Consider a right-angled triangle with a corresponding angle \theta.
 
intro.png
 
The three basic trigonometric ratios are:
 
  • Sine
  • Cosine
  • Tangent
 
The table below depicts the relation of reciprocal ratios with the right-angled triangle.
 
Name of the angle
Sine
Cosine
Tangent
Short form of the angle
\sin
\cos
\tan
Relationship
\sin \theta = \frac{\text{Opposite side}}{\text{Hypotenuse}}
\cos \theta = \frac{\text{Adjacent side}}{\text{Hypotenuse}}
\tan \theta = \frac{\text{Opposite side}}{\text{Adjacent side}}
Name of the reciprocal angle
Cosecant
Secant
Cotangent
Short form of the angle
\text{cosec}
\sec
\cot
Measurements related to the right-angled triangle
sin.png
cos.png
tan.png
Relationship
\text{cosec}\,\theta = \frac{\text{Hypotenuse}}{\text{Opposite side}}
\sec \theta = \frac{\text{Hypotenuse}}{\text{Adjacent side}}
\cot \theta = \frac{\text{Adjacent side}}{\text{Opposite side}}
Relation with the basic ratio
\text{cosec}\,\theta = \frac{1}{\sin \theta}
 
or
 
\sin \theta = \frac{1}{\text{cosec}\,\theta}
\sec \theta = \frac{1}{\cos \theta}
 
or
 
\cos \theta = \frac{1}{\sec \theta}
\cot \theta = \frac{1}{\tan \theta}
 
or
 
\tan \theta = \frac{1}{\cot \theta}
 
We can write certain identities based on these relationships.
 
  • Identity 1:
\text{cosec}\,\theta \times \sin \theta = \text{cosec}\,\theta \times \frac{1}{\text{cosec}\,\theta}
 
= 1
 
Therefore, \text{cosec}\,\theta \cdot \sin  \theta= 1.
  • Identity 2:
\sec \theta \times \cos \theta = \sec \theta \times \frac{1}{\sec \theta}
 
= 1
 
Therefore, \sec \theta \cdot \cos \theta = 1.
  • Identity 3:
\cot \theta \times \tan \theta = \cot \theta \times \frac{1}{\cot \theta}
 
= 1
 
Therefore, \cot \theta \cdot \tan \theta = 1.