Posted - 01/20/2011 : 23:36:45 Hey there, so it has been a while since I have taken Calc, and now I find myself in Calc 3 contemplating my career choices. Needless to say, I need some help proving a simple derivative of a vector-valued function, as I have never dealt with these. Of course I never have time to meet with the teacher when I work all day, so here I am. SO the problem states if |r(t)| > 0 , then show that: (d/dt)|r(t)| = {(1/|r(t)|)*r(t)} * {(d/dt)r(t)}

What happens as |r(t)|=0 with {(d/dt)r(t)}?

I have never seen a vector function until the other day, and I'm always uncomfortable with the 'prove this' type of general equations.

Thanks in advance for the help!

2 L A T E S T R E P L I E S (Newest First)

maser22

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royhaas

Posted - 01/21/2011 : 12:51:54 I believe your second "*" is actually a dot product. Write r(t)=x(t)i+y(t)j+z(t)k and use that.