I have two points p1:(x1,y1) and p2:(x2,y2) and a curve(sometimes an arc, no specific shape) is drawn from p1 to p2

I have two points p1:(x1,y1) and p2:(x2,y2) and a curve(sometimes an arc,
no specific shape) is drawn from p1 to p2

I want to find the tangent angle at p2. I think y2-y1 / x2-x1 will give
the slope, if the points p1 and p2 are on a line. And is tan
((y2-y2)/(x2-x1)) gives the tangent angle ?? And also if p1 and p2 are on
an arc how can i get the angle of the tangent of the arc at p2 ?
Can anyone help me on this please ??