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## Main Question or Discussion Point

Let

How do we approach this one?

maybe:

...and then what?

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

**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