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1 Answer

At time t, Jack’s position is 5t miles east of X while Jill’s position is 8+4t miles south of X.

The distance s between them is √((5t)²+(8+4t)²)=√(41t²+64t+64), by Pythagoras.

ds/dt=(1/2)(82t+64)/√(41t²+64t+64) is the rate of change (speed) of distance between them.

After an hour, t=1, this expression has a value (1/2)(146)/√169=(1/2)(146)/13=73/13=5.62mph.

by Top Rated User (642k points)

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