why is the quadratic curve of this function not n-shaped? (displacement-time graph)

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i have to draw a displacement-time graph of a particle that goes from A to B and when it hits B it returns back to a point C in the opposite direction. the distance AB is 4.4m an the distance CB is 0.625m when found. so i have 2 suvat equations relating s to t. (i have found them) they are:

  1. $s = 3t - 0.4t^2$ for motion from A to B
  2. $s = -0.4t^2 + t$ for the opposite motion from B to C.

0<t<3.25(both inclusive)

so the first one is clearly an n-shaped curve. and the second one too. however in my book the answer thats given is, the first one forms an n-shaped curve and the second one forms a u-shaped curve. can anyone explain why please?

does it have anything to do with the motion from B to C being in the opposite direction?