The chain rule states that the derivative of f(g(x)) is f'(g(x))g'(x). In other words, it helps us differentiate composite functions. For example, sin(x) is a composite function because it can be constructed as f(g(x)) for f(x)=sin(x) and g(x)=x_. Using the chain rule and the derivatives of sin(x) and x_, we can then find the derivative of sin(x_). Created by Sal Khan.

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Thanks to all of you who support me on Patreon. You da real mvps! $1 per month helps!! 🙂 https://www.patreon.com/patrickjmt !! The Law of Cosines, Example 4. Here we use the law of cosines to help deduce an angle between the flightpath of two planes!

A train traveling east at 70 m/s approaches another train traveling west at 50 m/s. The two trains are 2400 meters apart. How long will it take for the two trains to approach each other?