Test 3 sols-1

Test 3 sols-1 - Name: _ Test #3 Applications of Derivatives...

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Name: ________________ Test #3 Applications of Derivatives Math 160 Calculators are permitted, but show all work. 1. Solve either of the problems below. A. A boat is tied to a dock as shown in the picture below. A winch on the dock is connected to the boat, and when the winch is turned, the rope is drawn in, and the boat moves closer to the dock. The top of the winch is 5 feet above the point where the rope attaches to the boat. When the winch is turned, the rope is pulled in at a constant rate of 2 ft per second. How fast is the boat approaching the dock when it is 12 feet away? y doesn't change, so, its rate of change is 0. r is decreasing by 2 ft/s, so its rate of change is -2 So, the boat is getting closer to the dock at a rate of 13/6 ft/sec. 5 ft. r y x x 2 + y 2 = r 2 When x = 12, r = 13 2 x dx dt 2 y dy dt = 2 r dr dt x dx dt y dy dt = r dr dt 12 dx dt 0 = 13 − 2 dx dt = 13 6
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B. For the graph of y 2 x 3 10 y 9 = 0 find the slope, dy dx , of the tangent line. At what point(s) does this graph have a horizontal tangent? At what point(s) does this graph have a vertical tangent? Solve for y ': The graph has a horizontal tangent when the numerator is 0, and a vertical tangent when the denominator is 0. Horizontal: so x = 0. We need the point ( x , y ), so we plug 0 in for x in the original equation and find y . y 2 10 y 9 = 0 This is a quadratic equation, giving y = -9 and y = -1. Thus, the graph has a horizontal tangent at (0, -1) and (0, 9). Vertical: 2 y 10 = 0 so y = -5. Plugging this in for y , we get 25 x 3 50 9 = 0 and x = 3 16 . The graph has a vertical tangent at 3 16 , 5 . 2. A fence is to be built to encolse a rectangular area of 800 square feet. The fence along three sides is
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This note was uploaded on 02/28/2012 for the course MATH 160 taught by Professor Staff during the Spring '08 term at Boise State.

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Test 3 sols-1 - Name: _ Test #3 Applications of Derivatives...

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