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## Main Question or Discussion Point

When do you know to use the chain rule??

I really don't understand what this means: dr/dt = dr/ds * ds/dt

Like in one example in the book they have:

r(s) = cos2si + sin2sj + e^-3sk where s = t^4

Then they find dr/dt using the chain rule. My question is why can't you just differentiate it normally by the individual components? How would that be different?

I really don't understand what this means: dr/dt = dr/ds * ds/dt

Like in one example in the book they have:

r(s) = cos2si + sin2sj + e^-3sk where s = t^4

Then they find dr/dt using the chain rule. My question is why can't you just differentiate it normally by the individual components? How would that be different?