Most people who have done maths in high school, would have heard of Pythagoras theorem.
This is used to work out the unknown side of a triangle, if you know the other 2 sides.
Here you can see the sides, A, B and C.
Now Pythagoras theorem states that A^2 + B^2 = C^2
So if you know any two sides, you add them in, rearrange the formula if needed, and then you can solve for the unkown sides.
So how would you use this in a game? What about collision detection? Using this you can find quite easily in a 2 dimensional plane when 2 points will meet.
They will meet when A^2 + B^2 = 0
Quite simple really, you take the position of A and B on the X axis and do the equation, then if it comes up with an answer of 0, you then take the position of A and B on the Y axis, then if that also comes to 0, they must be colliding.
So to put that in other words, we are finding the distance If the distance is nothing, then they are located in the same position.
Not sure if that is right, sounds right from my position, although it is 1:18 am.
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