The Tangent Function

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AP Precalculus › The Tangent Function

Questions 1 - 10
1

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 $\theta$?

$\theta=\arctan!\left(\dfrac{3}{2}\right)$

$\theta=\arctan!\left(\dfrac{2}{3}\right)$

$\theta=\arccos!\left(\dfrac{2}{3}\right)$

$\theta=\arcsin!\left(\dfrac{2}{3}\right)$

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.

2

Given tangent $\tan\theta=\dfrac{\sin\theta}{\cos\theta}$ and vertical asymptotes where $\cos\theta=0$, which equation represents all asymptotes of $y=\tan x$?

$x=2k\pi$

$x=\dfrac{\pi}{2}+k\pi$

$x=\dfrac{k\pi}{2}$

$x=k\pi$

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.

3

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 $h$?

$h=80\sin\theta$

$h=80\tan\theta$

$h=80\cos\theta$

$h=\dfrac{80}{\tan\theta}$

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.

4

Since $\tan x=\dfrac{\sin x}{\cos x}$, zeros occur when $\sin x=0$ and $\cos x\neq0$. Which set gives all zeros of $y=\tan x$?

$x=\dfrac{\pi}{2}+k\pi$

$x=\dfrac{k\pi}{2}$

$x=\dfrac{\pi}{4}+k\pi$

$x=k\pi$

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.

5

A surveyor uses $\tan\theta=\dfrac{\text{opposite}}{\text{adjacent}}$ to model an angle of elevation. If $\tan\theta=\dfrac{3}{4}$, which statement is correct?

Hypotenuse is 3 when adjacent is 4.

Adjacent is 3 when hypotenuse is 4.

Opposite is 3 when adjacent is 4.

Opposite is 4 when adjacent is 3.

Explanation

This question tests AP Precalculus understanding of the tangent function's properties, specifically interpreting tangent ratios in practical surveying contexts. When tan θ = 3/4, this means the opposite side is 3 units for every 4 units of the adjacent side, following the definition tan θ = opposite/adjacent. In this question, students must correctly interpret the given ratio tan θ = 3/4 in terms of the triangle's sides. Choice B is correct because it accurately states that the opposite side is 3 when the adjacent side is 4, matching the given tangent value. Choice A is incorrect because it reverses the ratio, stating opposite is 4 when adjacent is 3, which would give tan θ = 4/3, not 3/4. To help students: Practice writing tangent ratios in fraction form and identifying which number represents opposite versus adjacent. Use proportional reasoning to scale triangles while maintaining the same angle, showing that tan θ = 3/4 could also mean opposite = 6 when adjacent = 8.

6

A road’s grade uses slope, and tangent matches slope by $\tan\theta=\dfrac{\text{rise}}{\text{run}}$. Based on this, how does tangent relate to slope?

Tangent equals $\dfrac{\text{rise}}{\text{run}}$.

Tangent equals $\dfrac{\text{run}}{\text{rise}}$.

Tangent equals $\dfrac{\text{rise}}{\text{hypotenuse}}$.

Tangent equals $\dfrac{\text{hypotenuse}}{\text{run}}$.

Explanation

This question tests AP Precalculus understanding of the tangent function's properties, specifically its direct relationship to slope in practical applications. The tangent of an angle in a right triangle equals the ratio of the opposite side to the adjacent side, which corresponds exactly to rise over run in slope calculations. In this question, the road grade context connects mathematical concepts to real-world engineering applications. Choice B is correct because tangent equals rise/run, matching the standard definition of slope in coordinate geometry. Choice A is incorrect because it inverts the ratio to run/rise, which would give the cotangent rather than the tangent. To help students: Draw right triangles with various angles and calculate both tan θ and slope to see they're identical. Use physical models like ramps or stairs to demonstrate that steeper angles have larger tangent values, just like steeper lines have larger slopes.

7

In an angle-of-elevation setup, tangent is $\tan\theta=\dfrac{\sin\theta}{\cos\theta}$ and is undefined when $\cos\theta=0$. At which angle is $\tan\theta$ undefined?

$\theta=\dfrac{\pi}{2}$

$\theta=\dfrac{3\pi}{2}$

$\theta=\pi$

$\theta=\dfrac{\pi}{3}$

Explanation

This question tests AP Precalculus understanding of the tangent function's properties, specifically identifying where the function is undefined due to division by zero. The tangent function equals sin θ/cos θ, so it's undefined whenever the denominator cos θ equals zero, which first occurs at θ = π/2 in the standard domain. In this question, students must recognize that cos(π/2) = 0, making tan(π/2) undefined. Choice B is correct because at θ = π/2, cosine equals zero while sine equals one, creating a division by zero situation. Choice A is incorrect because cos(π/3) = 1/2, not zero, so tan(π/3) = √3 is well-defined. To help students: Create a table of special angles showing sin θ, cos θ, and tan θ values to identify patterns. Emphasize checking the denominator (cosine) for zeros when determining where tangent is undefined, and connect this to vertical asymptotes on the graph.

8

In a right-triangle navigation setup, $

tan\theta=\dfrac{\sin\theta}{\cos\theta}$; which equation gives the vertical asymptotes of tan $x$?

$x=\dfrac{\pi}{2}+2k\pi$

$x=k\pi$

$x=\dfrac{\pi}{2}+k\pi$

$x=2k\pi$

Explanation

This question tests AP Precalculus understanding of the tangent function's properties, specifically identifying where vertical asymptotes occur. The tangent function is defined as the ratio of sine to cosine, and vertical asymptotes occur where the denominator (cosine) equals zero. In this question, students must determine when cos(x) = 0, which happens at odd multiples of π/2. Choice B is correct because x = π/2 + kπ represents all odd multiples of π/2 where k is any integer, precisely where cosine equals zero. Choice A is incorrect because it represents multiples of π where cosine alternates between 1 and -1, not zero. To help students: Emphasize that vertical asymptotes occur when denominators equal zero. Practice identifying zeros of cosine by visualizing the unit circle or cosine graph.

9

A ramp rises 3 m over a 4 m run; based on tan $\theta=\dfrac{\sin\theta}{\cos\theta}$, how does tan relate to slope?

cos $\theta=\dfrac{\text{rise}}{\text{run}}$

sin $\theta=\dfrac{\text{rise}}{\text{run}}$

tan $\theta=\dfrac{\text{rise}}{\text{run}}$

tan $\theta=\dfrac{\text{run}}{\text{rise}}$

Explanation

This question tests AP Precalculus understanding of the tangent function's properties, specifically its relationship to slope in right triangles. The tangent function is defined as the ratio of sine to cosine, which in a right triangle context equals opposite over adjacent, or rise over run. In this question, the ramp scenario with 3m rise and 4m run provides a concrete application of tangent as slope. Choice A is correct because tan θ = rise/run directly matches the slope formula, making tangent the natural trigonometric function for calculating slopes and angles of inclination. Choice D is incorrect because it inverts the ratio, giving run/rise which would be cotangent, not tangent. To help students: Connect tangent to the slope formula m = rise/run from algebra. Use physical examples like ramps and ladders to reinforce the opposite/adjacent interpretation.

10

In navigation, tangent satisfies $\tan\theta=\dfrac{\sin\theta}{\cos\theta}$ and repeats every $\pi$ radians. What is the period of $y=\tan x$?

$\pi$

$\dfrac{\pi}{2}$

$2\pi$

$\dfrac{3\pi}{2}$

Explanation

This question tests AP Precalculus understanding of the tangent function's properties, specifically its fundamental period and how it differs from sine and cosine functions. The tangent function is periodic with period π, not 2π like sine and cosine, because tan(x + π) = tan(x) for all x in the domain. In this question, the navigation context emphasizes the practical importance of understanding periodicity for cyclic phenomena. Choice A is correct because the tangent function completes one full cycle every π radians, visible in its graph between consecutive asymptotes. Choice B is incorrect because it confuses tangent's period with that of sine and cosine, which have period 2π. To help students: Graph y = tan x alongside y = sin x and y = cos x to compare periods visually. Emphasize that tangent's period is half that of sine and cosine because both sin(x + π) and cos(x + π) change sign, making their ratio unchanged.

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