For an arbitrary motion in space, which of the following relations are true :
(a) `vec a`(average)`` = `1/2 [ vec v (t_1) + vec v (t_2)]`
(b) ` vec v `(average )`` = `[vec r (t_2) - vec r (t_1 ) ] // (t_2 -t_1)`
(c ) `vec v(t) = vec v (0) + vec a t`
(d) ` vec r (t) = vec r(0) + vec v (0) t + ( 1//2 ) vec a t^2`
(e) ` vec a_`(average)`` =`[ vec v( t_2) - vec v (t_2 ) ] // (t_2 -t_1)`
The average stands for average of the quantity over the time interval ` t_1` and t_2` ].