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Graphs of Inverse Trigonometric Functions

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Estimated time: 12 minutes
CBSE: Class 12

Introduction

Inverse trigonometric functions are used to find an angle when the value of a trigonometric ratio is known. Since trigonometric functions are many-to-one over their full domains, each function is first restricted to a suitable interval so that its inverse becomes well-defined. The graphs of inverse trigonometric functions are obtained by reflecting the appropriate restricted branch of the original trigonometric graph in the line y = x.

CBSE: Class 12

Graphs of Inverse Trigonometric Functions

1. \[y = \sin^{-1}x\]

   

  • Behavior: The graph is strictly increasing.

  • Key points: Passes through \[(-1, -\frac{\pi}{2})\], \[(0, 0)\], and \[(1, \frac{\pi}{2})\].

2. \[y = \cos^{-1}x\]

  • Behavior: The graph is strictly decreasing.

  • Key points: Passes through \[(-1, \pi)\], \[(0, \frac{\pi}{2})\], and \[(1, 0)\].

3. \[y = \text{cosec}^{-1}x\]

 

  • Asymptote: The x-axis (y = 0) is a horizontal asymptote as \[x \to \infty\] or \[x \to -\infty\].

  • Key points: The branches approach \[y = \frac{\pi}{2}\] as \[x \to \infty\] and \[y = -\frac{\pi}{2}\] as \[x \to -\infty\].

4. \[y = \sec^{-1}x\]

 

  • Behavior: The two branches are separated; one stays in the range \[[0, \frac{\pi}{2})\] and the other in \[(\frac{\pi}{2}, \pi]\].

  • Key points: Passes through \[(-1, \pi)\] and \[(1, 0).

5. \[y = \tan^{-1}x\]

 

  • Behavior: Strictly increasing and passes through the origin (0, 0).

  • Horizontal Asymptotes: \[y = -\frac{\pi}{2}\] and \[y = \frac{\pi}{2}\]
  • Symmetry: Symmetric about the origin (odd function).

6. \[y = \cot^{-1}x\]

  • Behavior: Strictly decreasing over its entire domain.

  • Horizontal Asymptotes: y = 0 and \[y = \pi\]
  • Key points: It crosses the y-axis at \[(0, \frac{\pi}{2})\].

CBSE: Class 12

Key Points: Graphs of Inverse Trigonometric Functions

Function Domain Range / Principal value Important note
\[y = \sin^{-1} x\] [-1, 1] \[[-\frac{\pi}{2}, \frac{\pi}{2}]\] Increasing function
\[y = \cos^{-1} x\] [-1, 1] \[[0, \pi]\] Decreasing function
\[y = \tan^{-1} x\] \[\mathbb{R}\] \[(-\frac{\pi}{2}, \frac{\pi}{2})\] Increasing function
\[y = \cot^{-1} x\] \[\mathbb{R}\] \[(0, \pi)\]

Decreasing function

\[y = \sec^{-1} x\] \[(-\infty, -1] \cup [1, \infty)\] \[[0, \pi] \setminus \{\frac{\pi}{2}\}\] Increasing function
\[y = \text{cosec}^{-1} x\] \[(-\infty, -1] \cup [1, \infty)\] \[[-\frac{\pi}{2}, \frac{\pi}{2}] \setminus \{0\}\] Decreasing function
CBSE: Class 12

construction

2.6 cm 2 cm 3.6 cm 4 cm 3.2 cm M A B D C P
KEY THEOREM

Perpendicular Bisector Property

A point lies on the perpendicular bisector of a line segment if and only if it is equidistant from the two endpoints of that segment.

① P lies on AC because we placed it on diagonal AC.
② P lies on ⊥ bisector of BC because we chose that intersection.
∴ PB = PC and P is on AC P is the required point.
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