Trigonometric Functions

Trigonometric functions are also known as a Circular Functions can be simply defined as the functions of an angle of a triangle i.e. the relationship between the angles and sides of a triangle are given by these trig functions. The formulas, table and definition of basic functions such as sin, cos and tan are given here. Also, the other three ratios like sec, cosec and cot, which can be represented in graphs as well, have been explained here. There are a number of trigonometric formula and identities which denotes the relation between the functions and help to find the angles of the triangle. 

Also, you will come across the table for where the value of these ratios is mentioned for some particular degrees.  And based on this table you will be able to solve many trigonometric examples and problems.

Sin, Cos, and Tan Functions

The angles of sine, cosine, and tangent are the primary classification of functions of trigonometry. And the three functions which are cotangent, secant and cosecant can be derived from the primary functions. Basically, the other three functions are often used as compare to the primary 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. We usually define the trigonometry with the help of the right-angled triangle.

Trigonometric Functions-Sin, Cos, Tan

Trigonometry Functions Formula

Let us discuss the formulas for functions of trigonometric ratios(sine, cosine and tangent) for a right-angled triangle:

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 =Opposite/Hypotenuse = 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 = Adjacent/Hypotenuse = AB/CA

Tan Function

The 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 = Opposite/Adjacent = CB/BA

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

Tan a = sin a/cos a

Secant, Cosecant and Cotangent Functions

Secant, cosecant (csc) and cotangent are the three additional 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) =  Hypotenuse/Adjacent = CA/AB

Cosec a = 1/(sin a) = Hypotenuse/Opposite = CA/CB

cot a = 1/(tan a) = Adjacent/Opposite = BA/CB

Trigonometric Functions Table

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

Trigonometric Ratios/

angle= θ in degrees

0 °                               30 °                 45 °                  60 °                

90 °

Sin θ 0 1/2 1/√2 √3/2 1
Cos θ 1 √3/2 1/√2 1/2 0
Tan θ 0 1/√3 1 √3
Cosec θ 2 √2 2/√3 1
Sec θ 1 2/√3 √2 2
Cot θ √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 are represented as arcsine, arccosine, arctangent, arccotangent, arcsecant, and arc cosecant.

Trigonometric Function Examples

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

Solution: Using the trigonometric table, we have

Sin 45° = 1/√2

Cos 30° = 1/2

Tan 60° = √3

Example 2: Evaluate Sin 105° degrees.

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

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

Therefore, sin 105° = sin (60° + 45°) = sin 60° × cos 45° + cos 60° × sin 45°

= √3/2 × 1/√2 + 1/2 × 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°. 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° and let AB = x miles

We know, tan C = opposite side/adjacent side

tan(20°) = x/10

or x = 10 × tan(20°)

or x = 10 × 0.36 = 3.6

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

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Practise This Question

Match the following:

Given sin x = 25 and x ϵ (0,Π2)

(p) cos x(1)52(q) tan x(2)212(r) cosec x(3)215(4)221

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