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March 1, 2015

Posted by **Mr. goodstuff** on Tuesday, January 17, 2012 at 11:53am.

- calculus -
**Reiny**, Tuesday, January 17, 2012 at 1:39pmmake a sketch

At a time of t hrs,

let the distance the police car is from the intersection be x miles

let the distance the speeding car is from the intersection be y miles

let the distance between them be d miles

d^2 = x^2 + y^2

2d dd/dt = 2x dx/dt + 2y dy/dt

d dd/dt = x dx/dt + y dy/dt

given: x = .6, y = .8 , dx/dt = -60 , dd/dt = 20

( I made dx/dt negative because the value of x is decreasing)

d^2 = .6^2 + .8^2 = 1

d = 1

1(20) = .6(-60) + .8dy/dt

20 + 36 = .8 dy/dt

dy/dt = 56/.8 = 70

The car was speeding at 70 mph

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