This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
A =  d v / dt  = (v2 - v1 ) / t

if v2 < v1,  then  a is negative.  always....

Only possibility that    a  can be positive   is that you choose a sign convention in such a way that  quantities in the direction of movement  are negative.  and the quantities in the opposite direction are positive.

Choose  the downward direction (vertically) as the positive  y axis.   If a stone is throne upwards with an initial velocity  u.  Then the displacement s = 0 at t = 0 and then it becomes more and more negative.  Hence,  velocity will be negative.    As the speed reduces,    change in velocity is  positive  ie., acceleration is positive.

2 3 2
please click on thanks blue link above