Chapter 6: Problem 74
Evaluate each expression exactly, if possible. If not possible, state why. $$\tan ^{-1}[\tan (8 \pi)]$$
Short Answer
Expert verified
The expression evaluates to 0.
Step by step solution
01
Understand the expression
The exercise asks us to evaluate the expression \(\tan^{-1}[\tan(8\pi)]\). This involves understanding how the \(\tan\) and \(\tan^{-1}\) functions interact.
02
Evaluate \(\tan(8\pi)\)
The tangent function \(\tan(\theta)\) has a period of \(\pi\). Therefore, \(\tan(8\pi) = \tan(0) = 0\) because \(8\pi\) is equivalent to 0 radian over complete cycles.
03
Apply the inverse tangent function
The inverse tangent function \(\tan^{-1}(x)\) gives the angle whose tangent is \(x\). We have \(\tan^{-1}(0)\). Tangent of angle 0 is 0, so \(\tan^{-1}(0) = 0\).
04
Conclusion
The expression \(\tan^{-1}[\tan(8\pi)]\) simplifies to \(0\), because \(\tan^{-1}(0) = 0\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Tangent Function
The tangent function, often denoted as \( \tan(\theta) \), is a fundamental trigonometric function. It is defined as the ratio of the sine and cosine functions: \( \tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)} \). This function relates an angle of a right triangle to the ratio of the length of the side opposite the angle to the side adjacent.
- Range: The range of the tangent function spans from \(-\infty\) to \(+\infty\), or all real numbers. This is because the values of the ratio \( \frac{\sin(\theta)}{\cos(\theta)} \) can vary widely as \( \theta \) changes.
- Behavior: Importantly, the tangent function is undefined when \( \cos(\theta) = 0 \), because division by zero in mathematics is undefined. Thus, tangent has vertical asymptotes where the angle corresponds to \( 90^\circ + k\times180^\circ \), where \( k \) is an integer.
Inverse Tangent
The inverse tangent, also denoted as \( \tan^{-1}(x) \) or \( \arctan(x) \), is the opposite of the tangent function. This function takes a real number \( x \) as its input and returns an angle \( \theta \) as its output, satisfying \( \tan(\theta) = x \).
- Range: The output, or range, of the inverse tangent function is restricted to \( (-\frac{\pi}{2}, \frac{\pi}{2}) \), or \(-90^\circ\) to \(90^\circ\). This restriction ensures that each output angle is unique for a corresponding \( x \).
- Usage: It is mainly used to determine an angle when the tangent value is known. For example, if \( \tan(\theta) = x \), then \( \theta = \tan^{-1}(x) \) gives the precise measure of the angle.
Periodicity of Tangent Function
One of the noteworthy properties of the tangent function is its periodicity. A function is periodic if it repeats its values in regular intervals or periods. The tangent function has a period of \( \pi \), which means it repeats its values every \( \pi \) radians.
- Implication: If you have \( \tan(\theta) \), then \( \tan(\theta + n\pi) = \tan(\theta) \) for any integer \( n \). This periodicity is due to the nature of the sine and cosine functions, which make up the tangent function and also show periodic behavior.
- Example in Problem: In the given problem, we evaluated \( \tan(8\pi) \). Using periodicity, we realize that this is equivalent to \( \tan(0) \), given \( 8\pi \) is a multiple of \( \pi \). Therefore, the function value returns to that of \( \tan(0) \), which is 0.