Two lovers have a spat and swear they will never see each other again. The girl walks due south at 6 mph while the boy walks 10 mph on a heading of North 60. Degrees West. How fast is the distance between them changing 30 minutes later?

Question

aum · Answer

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aum · Answer

After "t" hours, OG = 6*t miles
OB = 10*t miles.
Find GB using the law of cosines.
Then find the derivative with respect to t to find the rate of change.
Put t = 1/2 to find the rate of change half hour later.

anonymous · Answer

What formula do you use to find the derivative? I found GB and understand the last step.

anonymous · Answer

Into the derivative of the law of cos?