Inverse Trigonometric Formulas

Inverse Trigonometric Formulas: Trigonometry is a part of geometry, where we learn about the relationships between angles and sides of a right-angled triangle. In Class 11 and 12 Maths syllabus, you will come across a list of trigonometry formulas, based on the functions and ratios such as, sin, cos and tan. Similarly, we have learned about inverse trigonometry concepts also. The inverse trigonometric functions are written as sin-1x, cos-1x, cot-1 x, tan-1 x, cosec-1 x, sec-1 x. Now let us get the formulas related to these functions.

What is Inverse Trigonometric Function?

The inverse trigonometric functions are also known as the anti trigonometric functions or sometimes called as arcus functions or cyclometric functions. The inverse trigonometric functions of sine, cosine, tangent, cosecant, secant, and cotangent are used to find the angle of a triangle from any of the trigonometric functions. It is widely used in many fields like geometry, engineering, physics etc. But in most of the time, the convention symbol to represent the inverse trigonometric function using arc-prefix like arcsin(x), arccos(x), arctan(x), arccsc(x), arcsec(x), arccot(x). To determine the sides of a triangle when the remaining side lengths are known.

Consider, the function y = f(x), and x = g(y) then the inverse function is written as g = f-1,

This means that if y=f(x), then x = f-1(y).

Such that f(g(y))=y and g(f(y))=x.

Example of Inverse trigonometric functions: x= sin-1y

The list of inverse trigonometric functions with domain and range value is given below:

Functions Domain Range
Sin-1 x [-1, 1] [-π/2, π/2]
Cos-1x [-1, 1] [0, π/2]
Tan-1 x R (-π/2, π/2)
Cosec-1 x R-(-1,1) [-π/2, π/2]
Sec-1 x R-(-1,1) [0,π]-{ π/2}
Cot-1 x R [-π/2, π/2]-{0}

Inverse Trigonometric Formulas List

To solve the different types of inverse trigonometric functions, inverse trigonometry formulas are derived from some basic properties of trigonometry. The formula list is given below for reference to solve the problems.

S.No Inverse Trigonometric Formulas
1 sin-1(-x) = -sin-1(x), x ∈ [-1, 1]
2 cos-1(-x) = π -cos-1(x), x ∈ [-1, 1]
3 tan-1(-x) = -tan-1(x), x ∈ R
4 cosec-1(-x) = -cosec-1(x), |x| ≥ 1
5 sec-1(-x) = π -sec-1(x), |x| ≥ 1
6 cot-1(-x) = π – cot-1(x), x ∈ R
7 sin-1x + cos-1x = π/2 , x ∈ [-1, 1]
8 tan-1x + cot-1x = π/2 , x ∈ R
9 sec-1x + cosec-1x = π/2 ,|x| ≥ 1
10 sin-1(1/x) = cosec-1(x), if x ≥ 1 or x ≤ -1
11 cos-1(1/x) = sec-1(x), if x ≥ 1 or x ≤ -1
12 tan-1(1/x) = cot1(x), x > 0
13 tan-1 x + tan-1 y = tan-1((x+y)/(1-xy)), if the value xy < 1
14 tan-1 x – tan-1 y = tan-1((x-y)/(1+xy)), if the value xy > -1
15 2 tan-1 x = sin-1(2x/(1+x2)), |x| ≤ 1
16 2tan-1 x = cos-1((1-x2)/(1+x2)), x ≥ 0
17 2tan-1 x = tan-1(2x/(1-x2)), -1<x<1
18 3sin-1x = sin-1(3x-4x3)
19 3cos-1x = cos-1(4x3-3x)
20 3tan-1x = tan-1((3x-x3)/(1-3x2))
21 sin(sin-1(x)) = x, -1≤ x ≤1
22 cos(cos-1(x)) = x, -1≤ x ≤1
23 tan(tan-1(x)) = x, – ∞ < x < ∞.
24 cosec(cosec-1(x)) = x, – ∞ < x ≤ 1 or -1 ≤ x < ∞
25 sec(sec-1(x)) = x,- ∞ < x ≤ 1 or 1 ≤ x < ∞
26 cot(cot-1(x)) = x, – ∞ < x < ∞.
27 sin-1(sin θ) = θ, -π/2 ≤ θ ≤π/2
28 cos-1(cos θ) = θ, 0 ≤ θ ≤ π
29 tan-1(tan θ) = θ, -π/2 < θ < π/2
30 cosec-1(cosec θ) = θ, – π/2 ≤ θ < 0 or 0 < θ ≤ π/2
31 sec-1(sec θ) = θ, 0 ≤ θ ≤ π/2 or π/2< θ ≤ π
32 cot-1(cot θ) = θ, 0 < θ < π
33 \(\sin ^{-1}x +\sin ^{-1}y=\sin ^{-1}(x\sqrt{1-y^{2}}+y\sqrt{1-x^{2}}), if x, y \geq 0 and x^{2}+y^{2} \leq 1\)
34 \(\sin ^{-1}x +\sin ^{-1}y=\pi -\sin ^{-1}(x\sqrt{1-y^{2}}+y\sqrt{1-x^{2}})\), if x, y ≥ 0 and x2+y2>1.
35 \(\sin ^{-1}x +\sin ^{-1}y=\pi -\sin ^{-1}(x\sqrt{1-y^{2}}-y\sqrt{1-x^{2}})\), if x, y ≥ 0 and x2+y2≤1.
36 \(\sin ^{-1}x +\sin ^{-1}y=\pi -\sin ^{-1}(x\sqrt{1-y^{2}}-y\sqrt{1-x^{2}})\), if x, y ≥ 0 and x2 +y2>1.
37 \(\cos ^{-1}x +\cos ^{-1}y=\cos ^{-1}(xy-\sqrt{1-x^{2}}\sqrt{1-y^{2}})\), if x,

y >0 and x2+y2 ≤1.

38 \(\cos ^{-1}x +\cos ^{-1}y=\pi -\cos ^{-1}(xy-\sqrt{1-x^{2}}\sqrt{1-y^{2}})\), if x, y >0 and x2+y2>1.
39 \(\cos ^{-1}x +\cos ^{-1}y=\cos ^{-1}(xy+\sqrt{1-x^{2}}\sqrt{1-y^{2}})\), if x, y > 0 and x2+y2≤1.
40 \(\cos ^{-1}x +\cos ^{-1}y=\pi -\cos ^{-1}(xy+\sqrt{1-x^{2}}\sqrt{1-y^{2}})\),if x, y > 0 and x2 +y2>1.

The inverse trigonometric formula list helps the students to solve the problems in an easy way by applying those properties to find out the solutions.

For more information and to understand the trigonometry concepts, visit BYJU’S – The Learning App and also watch interactive videos to learn the concepts in an easy and engaging way.

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