Trigonometric Functions

Trigonometric functions can be simply defined as the functions of an angle i.e. the relationship between the angles and sides of a triangle are given by these trig functions. In trigonometry, there are 6 main functions which are sine, cosine, tangent, secant, cosecant and cotangent angles.

What are Trigonometric Functions

The angles of sine, cosine, and tangent are the primary classification of trigonometric functions. Consider the following diagram as a reference for an explanation of these three primary functions. This diagram can be referred to as the sin-cos-tan triangle.

Trigonometric Functions

Trigonometric Functions Formula

Formulas for right angled triangle are as follows:

Sine, cosine, and tangent

Sine Function

Sine function of an angle is the ratio between the opposite side length to that of the hypotenuse. From the above diagram, the value of sin will be:

Sin a = \(\frac{Opposite}{Hypotenuse}\) = \(\frac{CB}{CA}\)

Cos Function

Cos of an angle is the ratio of the length of the adjacent side to the length of the hypotenuse. From the above diagram, the cos function will be derived as follows.

Cos a = \(\frac{Adjacent}{Hypotenuse}\) = \(\frac{AB}{CA}\)

Tan Function

Tangent function is the ratio of the length of the opposite side to that of the adjacent side. It should be noted that the tan can also be represented in terms of sine and cos as their ratio. From the diagram taken above, the tan function will be the following.

Tan a = \(\frac{Opposite}{Adjacent}\) = \(\frac{CB}{BA}\)

Also, in terms of sine and cos, tan can be represented as:

Tan a = \(\frac{sin\ a}{cos\ a}\)

Secant, cosecant, and cotangent

Secant, cosecant (csc) and cotangent are the three additional trigonometric functions which are derived from the primary functions of sine, cos, and tan. The reciprocal of sine, cos, and tan are cosecant (csc), secant (sec), and cotangent (cot) respectively. The formula of each of these functions are given as:

Sec a = 1/(cos a) =  \(\frac{Hypotenuse}{Adjacent}\) = \(\frac{CA}{AB}\)

Cosec a = 1/(sin a) = \(\frac{Hypotenuse}{Opposite}\) = \(\frac{CA}{CB}\)

cot a = 1/(tan a) = \(\frac{Adjacent}{Opposite}\) = \(\frac{BA}{CB}\)

Trigonometric Functions Table

The trigonometric table for six functions, Sin, Cos, Tan, Cosec, Sec, Cot, are as :

Trigonometric Ratios/ angle= a degrees

0 ° 30 ° 45 ° 60 °

90 °

Sin a 0 1/2 1/√2 √3/2 1
Cos a 1 √3/2 1/√2 1/2 0
Tan a 0 1/√3 1 √3 Not Defined
Cosec a Not Defined 2 √2 2/√3 1
Sec a 1 2/√3 √2 2 Not Defined
Cot a Not defined √3 1 1/√3 0

Inverse Trigonometric Functions

Inverse functions are used to obtain an angle from any of the angle’s trigonometric ratios. Basically inverses of the sine, cosine, tangent, cotangent, secant, and cosecant functions. These functions are represented as arc sine, arc cosine, arc tangent, arc cotangent, arc secant, and arc cosecant.

Trigonometry Examples with Answers

Example 1: Find the values of Sin 45^0, Cos 30^0 and Tan 60^0.[all angles are in degrees)

Solution: Using trigonometric table, we have

Sin 45^0 = 1/√2

Cos 30^0 = 1/2

Tan 60^0 = √3

 

Example 2: Evaluate Sin 105^0 degrees.

Solution: Sin 105^0 can be written as sin (60^0 + 45^0) which is similar to sin (A + B).

We know that, the formula for sin (A + B) = sin A x cos B + cos A x sin B

Therefore, sin 105^0 = sin (60^0 + 45^0) = sin 60^0 x cos 45^0 + cos 60^0 x sin 45^0

= √3/2 x 1/√2 + 1/2 x 1/√2

= √3/2√2 + 1/2√2

= (√2 + √6)/4

 

Example 3: A boy sees a bird sitting on a tree at an angle of elevation of 20^0. If boy is standing 10 miles away from the tree, at what height bird is sitting?

Solution: Consider ABC a right triangle, A is a bird’s location, B = tree is touching the ground and C = boy’s location.

So BC 10 miles, angle C = 20^0 and let AB = x miles

We know, tan C = opp/adj

tan(20^0) = x/10

or x = 10 x tan(20^0)

or x = 10 x 0.36 = 3.6

Bird is sitting at the height of 3.6 miles from the ground.

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Practise This Question

In any ΔABC, the least value of (sin2A+sin A+1sin A) is