Write each formula as an English phrase using the word varies or proportional. r = d/t, where r is the speed when traveling d miles in t hours.
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1. Equations & Inequalities
Rational Equations
Problem 31
Textbook Question
Solve each problem. Distance to the HorizonThe distance that a person can see to the horizon on a clear day from a point above the surface of Earth varies directly as the square root of the height at that point. If a person 144 m above the surface of Earth can see 18 km to the horizon, how far can a person see to the horizon from a point 64 m above the surface?
Verified step by step guidance1
Identify the relationship given: the distance to the horizon \(d\) varies directly as the square root of the height \(h\). This can be written as the equation \(d = k \sqrt{h}\), where \(k\) is the constant of proportionality.
Use the information given to find the constant \(k\). Substitute \(d = 18\) km and \(h = 144\) m into the equation: \$18 = k \sqrt{144}$.
Simplify the square root: \(\sqrt{144} = 12\), so the equation becomes \$18 = 12k\(. Solve for \)k$ by dividing both sides by 12.
Now that you have the value of \(k\), use it to find the distance \(d\) when the height \(h\) is 64 m. Substitute \(k\) and \(h = 64\) into the formula: \(d = k \sqrt{64}\).
Simplify \(\sqrt{64} = 8\), then multiply by \(k\) to find the distance \(d\) to the horizon from 64 m above the surface.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Direct Variation
Direct variation describes a relationship where one quantity changes proportionally with another. In this problem, the distance to the horizon varies directly as the square root of the height, meaning distance = k * √height for some constant k. Understanding this helps set up the equation to find unknown values.
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Square Root Function
The square root function involves taking the root of a number, which in this context relates height to distance. Since distance depends on the square root of height, recognizing how to manipulate and calculate square roots is essential for solving the problem accurately.
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Solving for a Constant of Variation
To solve direct variation problems, you first find the constant of variation (k) using known values. Once k is found, it can be used to calculate unknown distances or heights. This step is crucial for applying the direct variation formula to new data points.
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