let "a" be the point in
then the point must also be on the tangent line.
so we can now compute the slope using these 2 points
but we also know that the slope must be equal to the derivative evaluated at a so we get
We now have a system of equations in "m" and "a"
setting them equal gives
as far as I know (any input we be awsome )
this doesn't have a closed form solution(there may be another way )
but I solved the equation numericlly with Maple and it gives
this is in radians.
I hope this helps.