Ch. 5 - Trigonometric Identities

Lial12th EditionTrigonometryISBN: 9780136552161Not the one you use?Change textbook

Lial 12th Edition

Ch. 5 - Trigonometric Identities

Problem 5.RE..6

Chapter 6, Problem 5.RE..6

For each expression in Column I, choose the expression from Column II that completes an identity.
6. sec² x = ____

II
A. sin ^2 x/cos ^2 x
B.1/(sec ^2 x)
C. sin (-x)
D. csc ^2 x-cot ^2 x + sin ^2 x
E. tan x

Verified step by step guidance

Recall the Pythagorean identity involving secant and tangent: \(\sec^2 x = 1 + \tan^2 x\).

Understand that this identity comes from dividing the fundamental identity \(\sin^2 x + \cos^2 x = 1\) by \(\cos^2 x\).

Rewrite the expression \(\sec^2 x\) in terms of tangent using the identity: \(\sec^2 x = 1 + \tan^2 x\).

Compare the given expression \(\sec^2 x\) with the options in Column II to find the one that matches \(1 + \tan^2 x\).

Select the expression from Column II that completes the identity as \(1 + \tan^2 x\).

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Key Concepts

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

Pythagorean Identity

The Pythagorean identities relate the squares of sine, cosine, and secant functions. One key identity is 1 + tan²x = sec²x, which expresses sec²x in terms of tan²x. This identity is fundamental for transforming and simplifying trigonometric expressions.

Definition of Secant Function

Secant (sec x) is the reciprocal of cosine, defined as sec x = 1/cos x. Understanding this reciprocal relationship helps in manipulating expressions involving sec²x and connecting them to other trigonometric functions like cosine and tangent.

Trigonometric Function Squares

Squaring trigonometric functions, such as sec²x or tan²x, is common in identities and equations. Recognizing how these squares relate through identities allows for simplification and solving of trigonometric problems effectively.

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Related Practice

Textbook Question

Match each expression in Column I with its value in Column II.

(2 tan (π/3))/(1 - tan² (π/3))

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Use the given information to find cos(x - y).

sin y = - 2/3, cos x = -1/5, x in quadrant II, y in quadrant III

Textbook Question

For each expression in Column I, use an identity to choose an expression from Column II with the same value. Choices may be used once, more than once, or not at all.

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Textbook Question

Match each expression in Column I with its equivalent expression in Column II.

(tan (π/3) - tan (π/4))/(1 + tan (π/3) tan (π/4))

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Textbook Question

Use the given information to find sin(x + y).

sin y = - 2/3 , cos x = - 1/5, x in quadrant II, y in quadrant III

Textbook Question

Match each expression in Column I with its equivalent expression in Column II.

sin 60° cos 45° - cos 60° sin 45°

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