Show that for a particle moving with velocity v(t), if v . v'=0
then the speed v is constant.
The Attempt at a Solution
Let v = (v1,v2,...,vn)
and let v'= (v'1,v'2,...,v'n)
v . v'= v1v'1 + v2v'2 + ... + vnv'n = 0
This is the only way i can think of to go about it but i'm stuck here. What do i do to show v is constant when v.v'=0?