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Ch. 6 - Inverse Circular Functions and Trigonometric Equations
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161, 9780135440780, 9780136881117, 9780135440827, 9780135924891Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 103

Write each trigonometric expression as an algebraic expression in u, for u > 0.
sec (arccot (√4―u² )/ u)

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1
Recognize that the expression is \( \sec(\arccot(\frac{\sqrt{4 - u^2}}{u})) \). Let \( \theta = \arccot\left(\frac{\sqrt{4 - u^2}}{u}\right) \). This means \( \cot \theta = \frac{\sqrt{4 - u^2}}{u} \).
Recall the definition of cotangent: \( \cot \theta = \frac{\text{adjacent}}{\text{opposite}} \). So, we can think of a right triangle where the adjacent side is \( \sqrt{4 - u^2} \) and the opposite side is \( u \).
Find the hypotenuse of this right triangle using the Pythagorean theorem: \( \text{hypotenuse} = \sqrt{(\sqrt{4 - u^2})^2 + u^2} = \sqrt{4 - u^2 + u^2} = \sqrt{4} = 2 \).
Recall that \( \sec \theta = \frac{\text{hypotenuse}}{\text{adjacent}} \). Using the triangle sides, \( \sec \theta = \frac{2}{\sqrt{4 - u^2}} \).
Therefore, the original expression \( \sec(\arccot(\frac{\sqrt{4 - u^2}}{u})) \) can be written algebraically as \( \frac{2}{\sqrt{4 - u^2}} \).

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Representing the angle from an inverse trig function as a right triangle allows expressing trigonometric functions in terms of side lengths. Using the given expression inside arccot, one can assign sides and use the Pythagorean theorem to rewrite sec(arccot(...)) as an algebraic expression in u.
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