The Tangent Function
Help Questions
AP Precalculus › The Tangent Function
The zeros of the function $$f(x) = \tan(x)$$ occur at which values of $$x$$?
At $$x = \frac{\pi}{4} + \frac{k\pi}{2}$$ for any integer $$k$$.
At $$x = \frac{\pi}{2} + k\pi$$ for any integer $$k$$.
At $$x = 2k\pi$$ for any integer $$k$$.
At $$x = k\pi$$ for any integer $$k$$.
Explanation
The zeros of $$\tan(x) = \frac{\sin(x)}{\cos(x)}$$ occur when the numerator, $$\sin(x)$$, is equal to 0, provided the denominator is not also 0. The function $$\sin(x)$$ is zero at all integer multiples of $$\pi$$. At these values, $$\cos(x)$$ is either 1 or -1, so the denominator is not zero.
The function $$h(x) = a\tan(x)$$ is a transformation of the parent tangent function. If $$a = -2$$, which of the following describes the transformation?
A vertical compression by a factor of 2 and a reflection across the y-axis.
A vertical stretch by a factor of 2 and a translation 2 units down.
A vertical stretch by a factor of 2 and a reflection across the x-axis.
A horizontal stretch by a factor of 2 and a reflection across the x-axis.
Explanation
For a function $$y = af(x)$$, the parameter $$a$$ causes a vertical stretch by a factor of $$|a|$$. If $$a$$ is negative, it also causes a reflection across the x-axis. In this case, $$a=-2$$, so there is a vertical stretch by a factor of 2 and a reflection across the x-axis.
An equation for one of the vertical asymptotes of the function $$g(x) = \tan(\frac{1}{4}x)$$ is $$x=2\pi$$. What is the equation of the next vertical asymptote for increasing values of $$x$$?
$$x = 10\pi$$
$$x = 6\pi$$
$$x = 3\pi$$
$$x = 4\pi$$
Explanation
The period of $$g(x) = \tan(\frac{1}{4}x)$$ is $$\frac{\pi}{|b|} = \frac{\pi}{1/4} = 4\pi$$. The vertical asymptotes of a tangent function are separated by a distance equal to its period. If one asymptote is at $$x=2\pi$$, the next one for increasing $$x$$ will be at $$x = 2\pi + \text{period} = 2\pi + 4\pi = 6\pi$$.
The function $$f(x) = \tan(x)$$ is an odd function. Which of the following equations must be true for all values of $$x$$ in the domain of $$f$$?
$$f(-x) = f(x)$$
$$f(x) = f(x+\pi)$$
$$f(-x) = -f(x)$$
$$f(x) = \frac{1}{f(x)}$$
Explanation
The definition of an odd function is that $$f(-x) = -f(x)$$ for all $$x$$ in its domain. This corresponds to symmetry about the origin, which the tangent function possesses. Choice B defines an even function. Choice C is the definition of a periodic function with period $$\pi$$, which is true for tangent but is not the definition of an odd function.
The function $$f(x) = \tan(x)$$ can be expressed as the ratio $$f(x) = \frac{\sin(x)}{\cos(x)}$$. The function $$g(x) = \sin(x)$$ has a period of $$2\pi$$ and the function $$h(x) = \cos(x)$$ has a period of $$2\pi$$. Why is the period of $$f(x) = \tan(x)$$ equal to $$\pi$$ rather than $$2\pi$$?
Because the values of tangent in quadrant I are the reciprocals of values in quadrant IV.
Because the period of a ratio of functions is always half the period of the individual functions.
Because the tangent function has asymptotes which restrict the period to be smaller than $$2\pi$$.
Because both $$\sin(x+\pi) = -\sin(x)$$ and $$\cos(x+\pi) = -\cos(x)$$, their ratio remains unchanged.
Explanation
The period is the smallest positive value $$P$$ such that $$f(x+P)=f(x)$$. Let's test $$P=\pi$$. $$\tan(x+\pi) = \frac{\sin(x+\pi)}{\cos(x+\pi)} = \frac{-\sin(x)}{-\cos(x)} = \frac{\sin(x)}{\cos(x)} = \tan(x)$$. Since the function values repeat every $$\pi$$ units and this is the smallest such positive value, the period is $$\pi$$.
Which statement accurately describes the behavior of the tangent function, $$f(x) = \tan(x)$$, on the interval $$(\frac{\pi}{2}, \frac{3\pi}{2})$$?
The function increases on $$(\frac{\pi}{2}, \pi)$$ and then decreases on $$(\pi, \frac{3\pi}{2})$$.
The function is always increasing on the entire interval.
The function is always decreasing on the entire interval.
The function decreases on $$(\frac{\pi}{2}, \pi)$$ and then increases on $$(\pi, \frac{3\pi}{2})$$.
Explanation
The interval $$(\frac{\pi}{2}, \frac{3\pi}{2})$$ is one full period of the tangent function, between two consecutive vertical asymptotes. Throughout any such interval, the tangent function is strictly increasing.
In architecture, tan $\theta=\dfrac{\sin\theta}{\cos\theta}$; from 30 m away, a 20 m tower gives $\tan\theta=\dfrac{20}{30}$. What is $\theta$?
$\theta=\arccos!\left(\dfrac{2}{3}\right)$
$\theta=\arctan!\left(\dfrac{2}{3}\right)$
$\theta=\arcsin!\left(\dfrac{2}{3}\right)$
$\theta=\arctan!\left(\dfrac{3}{2}\right)$
Explanation
This question tests AP Precalculus understanding of the tangent function's properties, specifically using inverse tangent to find angles from known ratios. The tangent function is defined as the ratio of sine to cosine, and its inverse function arctan returns the angle whose tangent equals a given value. In this question, the architectural context with a 20m tower viewed from 30m away creates tan θ = 20/30 = 2/3. Choice A is correct because θ = arctan(2/3) properly uses the inverse tangent function to find the angle whose tangent equals 2/3. Choice D is incorrect because it inverts the fraction to 3/2, which would represent the angle if viewing from 20m away at a 30m tower. To help students: Emphasize that arctan 'undoes' the tangent function to recover angles. Practice setting up the opposite/adjacent ratio correctly before applying inverse tangent.
Given tangent $\tan\theta=\dfrac{\sin\theta}{\cos\theta}$ and vertical asymptotes where $\cos\theta=0$, which equation represents all asymptotes of $y=\tan x$?
$x=\dfrac{k\pi}{2}$
$x=\dfrac{\pi}{2}+k\pi$
$x=2k\pi$
$x=k\pi$
Explanation
This question tests AP Precalculus understanding of the tangent function's properties, specifically identifying where vertical asymptotes occur based on the function's definition. The tangent function is defined as sin θ/cos θ, which means it becomes undefined wherever cos θ = 0, creating vertical asymptotes at these points. In this question, students must identify all locations where cosine equals zero, which occurs at odd multiples of π/2. Choice C is correct because x = π/2 + kπ represents all odd multiples of π/2 (like π/2, 3π/2, 5π/2, etc.), which are precisely where cosine equals zero. Choice A is incorrect because x = kπ includes points like 0 and π where cosine equals 1 or -1, not zero. To help students: Draw the cosine graph and mark all zeros to visualize asymptote locations. Practice converting between different representations of periodic points, emphasizing that π/2 + kπ captures all odd multiples of π/2.
A drone observes a lighthouse: horizontal distance 80 m, angle of elevation $\theta$. Using tangent as $\tan\theta=\dfrac{\sin\theta}{\cos\theta}$, which equation finds the height $h$?
$h=80\tan\theta$
$h=\dfrac{80}{\tan\theta}$
$h=80\sin\theta$
$h=80\cos\theta$
Explanation
This question tests AP Precalculus understanding of the tangent function's properties, specifically applying it to solve real-world height problems using angle of elevation. The tangent of an angle equals opposite over adjacent in a right triangle, so when viewing upward at angle θ from a horizontal distance, tan θ = height/horizontal distance. In this question, the drone is 80 m away horizontally and looks up at angle θ to see the lighthouse top, forming a right triangle. Choice C is correct because rearranging tan θ = h/80 gives h = 80 tan θ, properly using tangent to find height from horizontal distance and angle. Choice A is incorrect because h = 80 sin θ would require knowing the hypotenuse, not just the horizontal distance. To help students: Draw the scenario as a right triangle, labeling the 80 m as adjacent to θ and h as opposite. Practice setting up tangent ratios before solving, emphasizing that tangent relates the two legs of a right triangle, not involving the hypotenuse.
Since $\tan x=\dfrac{\sin x}{\cos x}$, zeros occur when $\sin x=0$ and $\cos x\neq0$. Which set gives all zeros of $y=\tan x$?
$x=\dfrac{\pi}{2}+k\pi$
$x=\dfrac{\pi}{4}+k\pi$
$x=k\pi$
$x=\dfrac{k\pi}{2}$
Explanation
This question tests AP Precalculus understanding of the tangent function's properties, specifically locating its zeros based on the quotient definition. Since tan x = sin x/cos x, the function equals zero when the numerator sin x = 0 and the denominator cos x ≠ 0, which occurs at integer multiples of π. In this question, students must identify where sin x = 0 while ensuring cos x ≠ 0 to avoid undefined points. Choice C is correct because x = kπ represents all integer multiples of π (0, ±π, ±2π, etc.), where sine equals zero and cosine equals ±1. Choice A is incorrect because x = π/2 + kπ represents the asymptotes where cos x = 0, not the zeros of tangent. To help students: Graph y = sin x, y = cos x, and y = tan x together to visualize where tangent crosses the x-axis. Emphasize that zeros occur where the numerator is zero but the denominator isn't, distinguishing zeros from undefined points.