# Vector Calculus

Hey... i was hopeing somebody can help me with a homework question... its about vector calc.... taking the deriviative.

d/dx[r(t) dot r(t)] = r'(t) dot r(t) + r(t) dot r'(t) = 2r'(t) dot r(t)

I know it sounds sillly, but i was just wondering how on earth they got
2r'(t) dot r(t) ????

## Answers and Replies

Hurkyl
Staff Emeritus
Gold Member
Well, go through the list of properties of the dot product -- any of them look useful?

robphy
Homework Helper
Gold Member
Another approach... what must be true for that last equality
r'(t) dot r(t) + r(t) dot r'(t) = 2r'(t) dot r(t)
to happen (assuming that each side is correct)?
This should lead to the property hinted by Hurkyl.

Okay i see it now.

It comes from the property....

a dot (b + c) = a dot b + a dot c

:)

Thanks for poinitng that out...

Hurkyl
Staff Emeritus