Concept Check Suppose that the point (x, y) is in the indicated quadrant. Determine whether the given ratio is positive or negative. Recall that r = √(x² + y²) .(Hint: Drawing a sketch may help.) II , y/x
Table of contents
- 0. Review of College Algebra4h 45m
- 1. Measuring Angles40m
- 2. Trigonometric Functions on Right Triangles2h 5m
- 3. Unit Circle1h 19m
- 4. Graphing Trigonometric Functions1h 19m
- 5. Inverse Trigonometric Functions and Basic Trigonometric Equations1h 41m
- 6. Trigonometric Identities and More Equations2h 34m
- 7. Non-Right Triangles1h 38m
- 8. Vectors2h 25m
- 9. Polar Equations2h 5m
- 10. Parametric Equations1h 6m
- 11. Graphing Complex Numbers1h 7m
2. Trigonometric Functions on Right Triangles
Trigonometric Functions on Right Triangles
Problem 51
Textbook Question
An equation of the terminal side of an angle θ in standard position is given with a restriction on x. Sketch the least positive such angle θ , and find the values of the six trigonometric functions of θ . See Example 3. 2x + y = 0 , x ≥ 0
Verified step by step guidance1
Rewrite the given equation of the terminal side in slope-intercept form to understand the line better. Starting with the equation \$2x + y = 0\(, solve for \)y\( to get \)y = -2x$.
Since the terminal side lies on the line \(y = -2x\) with the restriction \(x \geq 0\), consider a point on this line where \(x\) is positive. For simplicity, choose \(x = 1\), then \(y = -2(1) = -2\). This point \((1, -2)\) lies on the terminal side.
Determine the angle \(\theta\) in standard position whose terminal side passes through the point \((1, -2)\). Use the definition of tangent: \(\tan(\theta) = \frac{y}{x} = \frac{-2}{1} = -2\). Since \(x \geq 0\) and \(y < 0\), the point is in the fourth quadrant, so \(\theta\) is the least positive angle between \$0$ and \(2\pi\) with \(\tan(\theta) = -2\).
Calculate the six trigonometric functions of \(\theta\) using the coordinates of the point \((1, -2)\). First, find the radius \(r = \sqrt{x^2 + y^2} = \sqrt{1^2 + (-2)^2} = \sqrt{1 + 4} = \sqrt{5}\). Then, use the definitions: \(\sin(\theta) = \frac{y}{r}\), \(\cos(\theta) = \frac{x}{r}\), \(\tan(\theta) = \frac{y}{x}\), \(\csc(\theta) = \frac{r}{y}\), \(\sec(\theta) = \frac{r}{x}\), and \(\cot(\theta) = \frac{x}{y}\).
Summarize the values of the six trigonometric functions based on the point and radius found, keeping in mind the signs of each function in the fourth quadrant.
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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 is determined by rotating the initial side counterclockwise by the angle θ. Understanding this helps in visualizing and sketching the angle based on given line equations.
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Equation of a Line and Angle Determination
The terminal side of the angle lies along a line given by an equation, here 2x + y = 0. By rewriting the line in slope-intercept form, the slope corresponds to the tangent of the angle θ. The restriction x ≥ 0 limits the terminal side to the right half-plane, ensuring the least positive angle is found.
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Six Trigonometric Functions
The six trigonometric functions—sine, cosine, tangent, cosecant, secant, and cotangent—are ratios of the sides of a right triangle or coordinates on the unit circle. Once θ is identified, these functions can be calculated using the coordinates of a point on the terminal side or the slope of the line.
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Introduction to Trigonometric Functions
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