Complete Guide to Inverse Trigonometric Ratios

The world of trigonometry offers a symphony of ratios, angles, and triangles that intertwine to form the building blocks of many complex mathematical problems. One fascinating offshoot of basic trigonometry is the concept of 'Inverse Trigonometric Ratios'. If traditional trigonometry allows us to find sides from angles, its inverse counterpart lets us unveil angles from given side lengths. Ready to reverse your trigonometric thinking? Let's explore!

Complete Guide to Inverse Trigonometric Ratios

Step-by-step Guide: Inverse Trigonometric Ratios

Basics of Trigonometric Ratios:
Recall the primary trigonometric ratios:
\( \sin(\theta) \)
\( \cos(\theta) \)
\( \tan(\theta) \)
These ratios relate the angles in a right triangle to the lengths of its sides.

Introducing Inverse Trigonometric Ratios:
These are essentially the ‘opposites’ of the primary trigonometric functions. They allow us to determine an angle when we are given a side ratio. The notations are:
\( \sin^{-1}(x) \text{ or } \arcsin(x) \)
\( \cos^{-1}(x) \text{ or } \arccos(x) \)
\( \tan^{-1}(x) \text{ or } \arctan(x) \)

Domain and Range Considerations:
Inverse trigonometric functions have specific domains and ranges to ensure they remain functions. Knowing these can help avoid errors in calculations.

  • For \(\sin^{-1}(x)\):
    • Domain: \([-1,1]\)
    • Range: \([-\frac{\pi}{2}, \frac{\pi}{2}]\)
  • For \(\cos^{-1}(x)\):
    • Domain: \([-1,1]\)
    • Range: \([0, \pi]\)
  • For \(\tan^{-1}(x)\):
    • Domain: \((-∞,∞)\)
    • Range: \((-\frac{\pi}{2}, \frac{\pi}{2})\)


Example 1:
If the sine of an angle \( \alpha \) is \(0.5\), find the measure of \( \alpha \).

To find the angle, we’ll use the inverse sine function:
\( \alpha = \sin^{-1}(0.5) \)
\( \alpha \) is approximately \(30^\circ\).

Example 2:
A ladder leaning against a wall makes an angle \( \beta \) such that the tangent of \( \beta \) is \(2\). Find \( \beta \).

We’ll employ the inverse tangent function:
\( \beta = \tan^{-1}(2) \)
\( \beta \) is approximately \(63.43^\circ\).

Practice Questions:

  1. Find the angle \( \gamma \) if \(\cos(\gamma) = 0.866\).
  2. A slope descends at an angle \( \delta \) such that the sine of \( \delta \) is \(-0.707\). Determine \( \delta \).


  1. \( \gamma \) is approximately \(30^\circ\).
  2. \( \delta \) is approximately \(-45^\circ\).

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