@y-3
Y
commented
This is a very vague question. Are you asking for the definition of acceleration or a specific 2D kinematics equation?
on
What is the formula for acceleration?
@y-3
Y
commented
If you are talking about the second line of completing the square, #4# and #16# are negative because in the process of completing the square, we added in an extra #4# and #16#. So, for the #x# completing the square, we had #x^2-4x#, but we wanted to have #x^2-4x+4=(x-2)^2#. So, #x^2-4x=x^2-4x+4-4=(x-2)^2-4#. The same logic and process applies to the #y# case.