confused with vectors concept !! :/

okay at 2:30 of this video he explains that final speed is same as initial speed ive seen this come up before but have never been taught it when exactly is this applied and why?? im a bit confused at the concept and dont want to end up just randomley applying it in exam and failing please help !! thankss

http://www.examsolutions.net/a-level-maths-papers/worked-solution/worked-solution.php?paper_id=56&solution=5.1

Like he said, you don't need to use that, just ignore it. I have no idea what he means either, but what I think he means is that where he draws the arrow, displacement = 0. So technically if u is positive in the upward direction (from zero displacement) then it must be negative in the downward direction (from zero displacement).

yeah but thing is its come up in another question in my book so would like to understand the concept just in case :/

okay at 2:30 of this video he explains that final speed is same as initial speed ive seen this come up before but have never been taught it when exactly is this applied and why?? im a bit confused at the concept and dont want to end up just randomley applying it in exam and failing please help !! thankss

http://www.examsolutions.net/a-level-maths-papers/worked-solution/worked-solution.php?paper_id=56&solution=5.1

the motion of a particle in this type of question is symmetrical