Table of contents

0. Review of College Algebra4h 45m

Rationalizing Denominators
17m

Pythagorean Theorem & Basics of Triangles
17m

Basics of Graphing
30m

Functions
41m

Transformations
45m

Asymptotes
4m

Solving Linear Equations
31m

Solving Quadratic Equations
55m

Complex Numbers
41m

1. Measuring Angles40m

Angles in Standard Position
12m

Coterminal Angles
8m

Complementary and Supplementary Angles
10m

Radians
8m

2. Trigonometric Functions on Right Triangles2h 5m

Trigonometric Functions on Right Triangles
45m

Special Right Triangles
30m

Cofunctions of Complementary Angles
26m

Solving Right Triangles
23m

3. Unit Circle1h 19m

Defining the Unit Circle
14m

Trigonometric Functions on the Unit Circle
9m

Common Values of Sine, Cosine, & Tangent
11m

Reference Angles
38m

Reciprocal Trigonometric Functions on the Unit Circle
6m

4. Graphing Trigonometric Functions1h 19m

Graphs of the Sine and Cosine Functions
32m

Phase Shifts
14m

Graphs of Secant and Cosecant Functions
10m

Graphs of Tangent and Cotangent Functions
21m

5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m

Inverse Sine, Cosine, & Tangent
28m

Evaluate Composite Trig Functions
44m

Linear Trigonometric Equations
28m

6. Trigonometric Identities and More Equations2h 34m

Introduction to Trigonometric Identities
1h 4m

Sum and Difference Identities
1h 3m

Double Angle Identities
16m

Solving Trigonometric Equations Using Identities
9m

7. Non-Right Triangles1h 38m

Law of Sines
49m

Law of Cosines
30m

Area of SAS & ASA Triangles
19m

8. Vectors2h 25m

Geometric Vectors
28m

Vectors in Component Form
32m

Direction of a Vector
23m

Unit Vectors and i & j Notation
27m

Dot Product
22m

Cross Product
11m

9. Polar Equations2h 5m

Polar Coordinate System
29m

Convert Points Between Polar and Rectangular Coordinates
26m

Convert Equations Between Polar and Rectangular Forms
29m

Graphing Other Common Polar Equations
39m

10. Parametric Equations1h 6m

Graphing Parametric Equations
12m

Eliminate the Parameter
32m

Writing Parametric Equations
21m

11. Graphing Complex Numbers1h 7m

Graphing Complex Numbers
6m

Polar Form of Complex Numbers
22m

Products and Quotients of Complex Numbers
14m

Powers of Complex Numbers (DeMoivre's Theorem)
23m

2. Trigonometric Functions on Right Triangles

Trigonometric Functions on Right Triangles

Trigonometry

2. Trigonometric Functions on Right Triangles

Trigonometric Functions on Right Triangles

Previous problem

2:11 minutes

Problem 34

Textbook Question

Determine the signs of the trigonometric functions of an angle in standard position with the given measure. See Example 2.
―15°

Verified step by step guidance

Identify the quadrant in which the angle lies. Since the angle is -15°, it is a negative angle measured clockwise from the positive x-axis. To find its equivalent positive angle, add 360°: $-15° + 360° = 345°$. This places the angle in the fourth quadrant.

Recall the signs of the trigonometric functions in each quadrant. In the fourth quadrant: sine is negative, cosine is positive, and tangent is negative.

Determine the reference angle. The reference angle is the acute angle the terminal side makes with the x-axis. For 345°, the reference angle is \$360° - 345° = 15°$.

Use the reference angle to find the values of the trigonometric functions, keeping in mind their signs in the fourth quadrant. For example, $\sin(-15°) = -\sin(15°)$, $\cos(-15°) = \cos(15°)$, and $\tan(-15°) = -\tan(15°)$.

Summarize the signs: sine is negative, cosine is positive, tangent is negative for the angle -15°.

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Key Concepts

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

Standard Position of an Angle

An angle in standard position has its vertex at the origin and its initial side along the positive x-axis. The terminal side rotates from the initial side by the given angle measure, positive for counterclockwise and negative for clockwise rotation. Understanding this helps locate the angle on the coordinate plane.

Quadrants and Sign of Coordinates

The coordinate plane is divided into four quadrants, each determining the signs of x and y coordinates. Since trigonometric functions depend on these coordinates, knowing the quadrant of the terminal side is essential to determine the sign of sine, cosine, and tangent.

Signs of Trigonometric Functions by Quadrant

Sine, cosine, and tangent functions have specific signs in each quadrant: sine is positive in QI and QII, cosine in QI and QIV, and tangent in QI and QIII. Identifying the quadrant of the angle allows you to assign the correct sign to each trigonometric function.

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