Here we will show you the basic trigonometric identities. They are to be used only for triangles that have a right angle. If the triangle is not a right triangle, none of the formulas shown below are valid. It is extremely important to keep this in mind. A triangle is a right triangle if one of the angles is equal to 90 degrees.
First make sure you examine the diagram below so you understand what the opposite and adjacent sides are.
Sine function
sin Θ =
Opposite side
Hypotenuse
sin Θ1 =
Opposite side
Hypotenuse
|
sin Θ =
Leg 2
H
sin Θ1 =
Leg 1
H
|
Cosine function
cos Θ =
Adjacent side
Hypotenuse
cos Θ1 =
Adjacent side
Hypotenuse
|
cos Θ =
Leg 1
H
cos Θ1 =
Leg 2
H
|
Tangent function
tan Θ =
Opposite side
Adjacent
tan Θ1 =
Opposite side
Adjacent
|
tan Θ =
Leg 2
Leg 1
tan Θ1 =
Leg 1
Leg 2
|
Cotangent function
cotan Θ =
Adjacent side
Opposite side
cotan Θ1 =
Adjacent side
Opposite side
|
cotan Θ =
Leg 1
Leg 2
cotan Θ1 =
Leg 2
Leg 1
|
Secant function
sec Θ =
Hypotenuse
Adjacent side
sec Θ1 =
Hypotenuse side
Adjacent side
|
sec Θ =
H
Leg 1
sec Θ1 =
H
Leg 2
|
Cosecant function
csc Θ =
Hypotenuse
Opposite side
csc Θ1 =
Hypotenuse
Opposite side
|
csc Θ =
H
Leg 2
csc Θ1 =
H
Leg 1
|
The tangent is the ratio of the sine to the cosine.
The cotangent is the inverse of the tangent.
The cosecant is the inverse of the sine
The secant is the inverse of the cosine
Mar 16, 17 03:15 PM
Great lesson about the law of reflection. Crystal clear explanation
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