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**be a v.v.f -with the first and second derivatives**

*r(t)***and**

*r'***. Determine formula for**

*r''***-in terms of**

*d/dt [r.(r' x r'')]***:**

*r*How do we approach this one?

maybe:

**??**

*d/dt [r.(r' x r'')] = d/dt [r.r' x r.r''] = ((r'.r' + r.r'') x r'.r'') + (r.r' x (r'.r'' + r.r'''))*...and then what?

Is anyone able to give me a starting point -- or starting direction? -- thanks heaps