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Ch.12 - Parametric and Polar Curves
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Not the one you use?Change textbook
Chapter 12, Problem 12.2.85a

Navigating A plane is 150 miles north of a radar station, and 30 minutes later it is 60 degree east of north at a distance of 100 miles from the radar station. Assume the plane flies on a straight line and maintains constant altitude during this 30-minute period.
a. Find the distance traveled during this 30-minute period.

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First, represent the initial and final positions of the plane relative to the radar station using coordinate geometry. Place the radar station at the origin (0,0). Since the plane is initially 150 miles north, its initial coordinates are (0, 150).
Next, determine the coordinates of the plane after 30 minutes. The plane is 100 miles from the radar station at a direction 60 degrees east of north. To find the coordinates, use trigonometry: the north (y) component is \(100 \times \cos(60^\circ)\) and the east (x) component is \(100 \times \sin(60^\circ)\). So, the final coordinates are \((100 \sin(60^\circ), 100 \cos(60^\circ))\).
Calculate the exact final coordinates by evaluating the sine and cosine values: \(\sin(60^\circ) = \frac{\sqrt{3}}{2}\) and \(\cos(60^\circ) = \frac{1}{2}\). Substitute these to get the final position as \((100 \times \frac{\sqrt{3}}{2}, 100 \times \frac{1}{2})\).
Now, find the distance traveled by the plane by calculating the distance between the initial point \((0, 150)\) and the final point \((100 \times \frac{\sqrt{3}}{2}, 100 \times \frac{1}{2})\). Use the distance formula: \(d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}\).
Substitute the coordinates into the distance formula: \(d = \sqrt{\left(100 \times \frac{\sqrt{3}}{2} - 0\right)^2 + \left(100 \times \frac{1}{2} - 150\right)^2}\). Simplify inside the square root to express the distance traveled.

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Key Concepts

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

Vector Representation and Components

Understanding how to represent positions using vectors and breaking them into components is essential. Here, the plane's positions relative to the radar station can be expressed as vectors with north and east components, allowing calculation of displacement and direction.
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Law of Cosines

The Law of Cosines relates the lengths of sides of a triangle to the cosine of one of its angles. It is useful here to find the distance traveled by the plane when given two position vectors and the angle between them.
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Distance and Displacement in Plane Geometry

Calculating the distance traveled involves finding the magnitude of the displacement vector between two points. This requires applying geometric principles to determine the straight-line distance between the initial and final positions.
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Related Practice
Textbook Question

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b. Plot the (x, y) pairs in the table and the complete parametric curve, indicating the positive orientation (the direction of increasing t).


x=−t+6, y=3t−3; −5≤t≤5 

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a. Find the area of R

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Area of a sector of a hyperbola: Consider the region R bounded by the right branch of the hyperbola x²/a² - y²/b² = 1 and the vertical line through the right focus

a. What is the area of R?

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Channel flow Water flows in a shallow semicircular channel with inner and outer radii of 1 m and 2 m (see figure). At a point P(r,θ) in the channel, the flow is in the tangential direction (counterclock wise along circles), and it depends only on r, the distance from the center of the semicircles.


a. Express the region formed by the channel as a set in polar coordinates.

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Textbook Question

Volume of a hyperbolic cap Consider the region R bounded by the right branch of the hyperbola x²/a² - y²/b² = 1 and the vertical line through the right focus.

a. What is the volume of the solid that is generated when R is revolved about the x-axis?

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