Skip to main content
Ch. 6 - Inverse Circular Functions and Trigonometric Equations
Lial - Trigonometry 12th Edition
Lial12th EditionTrigonometryISBN: 9780136552161Not the one you use?Change textbook
Chapter 7, Problem 6.2.37

Solve each equation over the interval [0°, 360°). Write solutions as exact values or to the nearest tenth, as appropriate.
sec² θ tan θ = 2 tan θ

Verified step by step guidance
1
Start by writing down the given equation: \(\sec^{2} \theta \tan \theta = 2 \tan \theta\).
Recognize that \(\tan \theta\) is a common factor on both sides. To simplify, subtract \(2 \tan \theta\) from both sides to get: \(\sec^{2} \theta \tan \theta - 2 \tan \theta = 0\).
Factor out \(\tan \theta\) from the left side: \(\tan \theta (\sec^{2} \theta - 2) = 0\).
Set each factor equal to zero to find possible solutions: (1) \(\tan \theta = 0\) and (2) \(\sec^{2} \theta - 2 = 0\).
For (2), rewrite \(\sec^{2} \theta\) in terms of \(\tan^{2} \theta\) using the identity \(\sec^{2} \theta = 1 + \tan^{2} \theta\), then solve for \(\tan \theta\). Finally, find all \(\theta\) in \([0^\circ, 360^\circ)\) that satisfy these conditions.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Trigonometric Identities

Trigonometric identities are equations involving trigonometric functions that hold true for all values within their domains. In this problem, recognizing that sec²θ = 1 + tan²θ helps simplify and solve the equation by expressing all terms in a single trigonometric function.
Recommended video:
5:32
Fundamental Trigonometric Identities

Solving Trigonometric Equations

Solving trigonometric equations involves isolating the trigonometric function and finding all angle solutions within a specified interval. This often requires factoring, using identities, and considering the periodic nature of functions like tangent and secant.
Recommended video:
4:34
How to Solve Linear Trigonometric Equations

Interval and Solution Set for Angles

When solving trigonometric equations over [0°, 360°), it is essential to find all solutions within one full rotation of the unit circle. Understanding how to interpret and express solutions as exact values or decimal approximations ensures completeness and accuracy.
Recommended video:
04:46
Coterminal Angles