You need to differentiate the position function with respect to t to find the velocity of particle such that:

`(ds)/(dt) = cos t - sin t`

You need to find velocity at `t = pi/3` , hence, you should substitute `pi/3 ` for t in equation `(ds)/(dt) = cos t - sin t` such that:

`(ds)/(dt)|_(t=pi/3) = cos pi/3- sin pi/3`

`(ds)/(dt)|_(t=pi/3) = 1/2 - sqrt3/2`

`(ds)/(dt)|_(t=pi/3) = (1-sqrt3)/2`

**Hence, evaluating the velocity at `t = pi/3` yields `(ds)/(dt)|_(t=pi/3) = (1-sqrt3)/2` .**

b) You need to evaluate the speed at `t = pi/3` , such that:

speed = `|(1-sqrt3)/2| = (sqrt3-1)/2`

**Hence, evaluating the speed at `t = pi/3` yields speed `= |(1-sqrt3)/2| = (sqrt3-1)/2` .**

c) You need to differentiate the velocity function with respect to t to find the acceleration of particle such that: ` (dv)/(dt) = -sin t - cos t`

You need to find acceleration at `t = pi/3` , hence, you should substitute `pi/3 ` for t in equation `(dv)/(dt) =-sin t - cos t` such that:

`(dv)/(dt)|_(t=pi/3) = -sin pi/3 - cos pi/3`

`(dv)/(dt)|_(t=pi/3) = -sqrt3/2 - 1/2`

`(dv)/(dt)|_(t=pi/3) = -(sqrt 3 + 1)/2`

**Hence, evaluating the acceleration at `t = pi/3` yields `(dv)/(dt)|_(t=pi/3) = -(sqrt 3 + 1)/2.` **