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## Homework Statement

Show that for a particle moving with velocity

**v**(t), if

**v**.

**v'**=0

then the speed v is constant.

## Homework Equations

## The Attempt at a Solution

Let

**v**= (v

_{1},v

_{2},...,v

_{n})

and let

**v'**= (v'

_{1},v'

_{2},...,v'

_{n})

So,

**v**.

**v'**= v

_{1}v'

_{1}+ v

_{2}v'

_{2}+ ... + v

_{n}v'

_{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?