Mathematics: The police department uses a formula to determine the speed at which a car was going when the driver applied the brakes, by measuring the distance of the skid marks. The equation d = 0.0015r^2 + r models the distance, d, in feet traveled after applying the brakes in a car moving r miles per hour (r is the speed of the car). If the distance the car traveled after applying the brakes equals 88 feet, what, what was the speed of the car? * *Round your answer to the nearest hundredth miles per hour.

The police department uses a formula to determine

andybiersack154

14.02.2022

9514 1404 393

78.71 mph

Step-by-step explanation:

You're looking for the solution to ...

d = 88

0.0015r^2 +r = 88

0.0015r^2 +r -88 = 0

Using the quadratic formula*, we find ...

r = (-1 +√(1² -4(0.0015)(-88)))/(2×0.0015)

r = (-1 +√1.528)/0.003 = 0.236123/0.003 = 78.7077

The speed of the car was about 78.71 mph.

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* The quadratic formula will also give a negative answer of about -745 mph, which is not relevant to the situation.

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