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The domain of y=cos⁡−1(x2−4)y = \cos^{-1}(x^2 - 4) is

Solution

✅ Correct Option: 2

The domain consists of all x-values that can be input into the function.

For cos⁡−1\cos^{-1} (inverse cosine), the input must be between −1-1 and 11, inclusive.


Since the function is y=cos⁡−1(x2−4)y = \cos^{-1}(x^2 - 4), the expression (x2−4)(x^2 - 4) must satisfy:

−1≤x2−4≤1-1 \leq x^2 - 4 \leq 1


For the left inequality:

x2−4≥−1x^2 - 4 \geq -1

x2≥3x^2 \geq 3

∣x∣≥3|x| \geq \sqrt{3}

This gives: x≤−3x \leq -\sqrt{3} or x≥3x \geq \sqrt{3}


For the right inequality:

x2−4≤1x^2 - 4 \leq 1

x2≤5x^2 \leq 5

∣x∣≤5|x| \leq \sqrt{5}

This gives: −5≤x≤5-\sqrt{5} \leq x \leq \sqrt{5}


Both conditions must be satisfied simultaneously.

On the left side: x≤−3x \leq -\sqrt{3} and x≥−5x \geq -\sqrt{5} gives [−5,−3][-\sqrt{5}, -\sqrt{3}]

On the right side: x≥3x \geq \sqrt{3} and x≤5x \leq \sqrt{5} gives [3,5][\sqrt{3}, \sqrt{5}]


Domain: [−5,−3]∪[3,5][-\sqrt{5}, -\sqrt{3}] \cup [\sqrt{3}, \sqrt{5}]

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