Class CBSE Class 12 Mathematics Inverse Trigonometric Functions Q #943
KNOWLEDGE BASED
APPLY
2 Marks 2024 VSA
Find the domain of the function \(f(x)=\sin^{-1}(x^{2}-4).\) Also, find its range.
Explanation
Domain
We need the argument of the arcsine to be in $[-1, 1]$:$$-1 \le x^2 - 4 \le 1$$Add 4 to all parts:$$3 \le x^2 \le 5$$Taking the square root, we get two intervals:$$\sqrt{3} \le |x| \le \sqrt{5}$$This splits into positive and negative regions:$$x \in [-\sqrt{5}, -\sqrt{3}] \cup [\sqrt{3}, \sqrt{5}]$$
Range
From the inequality above, we know that as $x$ varies over the domain, the term $(x^2 - 4)$ covers the entire interval $[-1, 1]$.Therefore, $f(x)$ covers all possible values of $\sin^{-1}(u)$:$$y \in \left[-\frac{\pi}{2}, \frac{\pi}{2}\right]$$

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Step-by-Step Solution

Step 1: Determine the domain.

For the function \(f(x) = \sin^{-1}(x^2 - 4)\) to be defined, the argument of the inverse sine function must be between -1 and 1, inclusive. Therefore, we must have:

\(-1 \le x^2 - 4 \le 1\)

Step 2: Solve the inequality.

We can split this into two inequalities:

1. \(x^2 - 4 \le 1 \Rightarrow x^2 \le 5 \Rightarrow -\sqrt{5} \le x \le \sqrt{5}\)

2. \(x^2 - 4 \ge -1 \Rightarrow x^2 \ge 3 \Rightarrow x \le -\sqrt{3}\) or \(x \ge \sqrt{3}\)

Step 3: Combine the inequalities.

Combining these two conditions, we get the domain as:

\(-\sqrt{5} \le x \le -\sqrt{3}\) or \(\sqrt{3} \le x \le \sqrt{5}\)

In interval notation: \([-\sqrt{5}, -\sqrt{3}] \cup [\sqrt{3}, \sqrt{5}]\)

Step 4: Determine the range.

To find the range, we need to find the minimum and maximum values of \(x^2 - 4\) for \(x\) in the domain \([-\sqrt{5}, -\sqrt{3}] \cup [\sqrt{3}, \sqrt{5}]\).

When \(x = \pm \sqrt{3}\), \(x^2 - 4 = 3 - 4 = -1\). \(\sin^{-1}(-1) = -\frac{\pi}{2}\)

When \(x = \pm \sqrt{5}\), \(x^2 - 4 = 5 - 4 = 1\). \(\sin^{-1}(1) = \frac{\pi}{2}\)

Since the inverse sine function is continuous and increasing on the interval [-1, 1], the range of \(f(x)\) is \([-\frac{\pi}{2}, \frac{\pi}{2}]\).

Correct Answer: Domain: \([-\sqrt{5}, -\sqrt{3}] \cup [\sqrt{3}, \sqrt{5}]\), Range: \([-\frac{\pi}{2}, \frac{\pi}{2}]\)

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because the student needs to apply their knowledge of inverse trigonometric functions and inequalities to determine the domain and range of the given function.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding the concept of the domain and range of inverse trigonometric functions and how transformations affect them.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's understanding of the domain and range of inverse trigonometric functions, a topic covered in the textbook.