Big Ideas Math: Modeling Real Life, Grade 8
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Big Ideas Math: Modeling Real Life, Grade 8 View details
2. The Pythagorean Theorem
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Exercise 14 Page 385

Plot the points on a coordinate plane and then use the Pythagorean Theorem.

113 miles

Practice makes perfect
Let's review the given information before we try to find the distance between the shipyard and the cargo ship at 4:00PM. We know that objects detected by radar are plotted on a coordinate plane where each unit represents 1 mile and that the shipyard is located at (0,0). The radar showed a cargo ship at (0, 15) at 9:00AM and the same ship appeared at (16, 15) at 10:00AM.
cargo ship on the coordinate plane
Over the course of 1 hour, the cargo ship traveled from (0, 15) to (16, 15). Let's calculate the distance the ship traveled during that hour! Horizontal:&16- 0=16 Vertical:&15- 15=0

The ship traveled 16 miles in 1 hour. We know that the difference in time between 9:00AM and 4:00PM is 7 hours. Because we are told that the ship is traveling at a constant speed and in a constant direction, this means that ship travels 7 times further than during the first hour. 16* 7 = 112 The ship traveled 112 miles from point (0, 15) to point (112,15) and arrived at 4:00PM. We can add the point to our diagram.

The first quadrant of a coordinate plane with a vertical measure equal 15 between (0,0) and (0,15) and a horizonal measure equal 112 between (0,15) and (112,15)

The distance from the shipyard to the cargo ship at 9:00AM is 15 miles and the distance the cargo ship traveled from 9:00AM to 4:00PM is 112 miles. To find the distance between the shipyard and the cargo ship at 4:00PM, we will draw a triangle with vertices at (0,0), (0,15), and (112,15).

triangle

The distance between the shipyard at point (0,0) and the cargo ship at (112,15) is the hypotenuse of the right triangle. We can use the Pythagorean Theorem to find this distance. a^2+b^2=c^2 In the formula, a and b are the legs and c is the hypotenuse of a right triangle. We will now identify a, b, and c on the diagram.

identify sides of the triangle
Let's substitute these values into the formula.
a^2+b^2=c^2
15^2+ 112^2=c^2
â–Ľ
Solve for c
225+12 544=c^2
12 769=c^2
sqrt(12 769)=c
c=sqrt(12 769)
c=113
The cargo ship is 113 miles away from the shipyard at 4:00PM.