How to determine the car's deceleration at a point along a curve?

[sophiecentaur]

this is when two lines meet, they form right angles.

Unless you state the whole thing, it’s meaningless. There are two pairs of lines involved. Read that helpful link. It states the actual theorem.

 

[JesseProbst]

Err, ok, thanks, I'll check it

 

[Lnewqban]

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The problem here is that my geometry bag is very weak, I didn't have any geometry in HS, will fix that sooner or later but anyway.
...

I have found these two websites about Geometry very interesting:
https://www.mathsisfun.com/geometry/index.html

https://www.mathopenref.com/tocs/triangletoc.html

Those are inter-active, and you can play as you learn.