Question

At x=15, y=250. so, please tell me if the red line is the tangent line of point (15,250)

Answer 1

A tangent is a straight line that touches a curve at a point but but does not cross it at that point.

The graph below is a tangent as it is only touching the line at the point of tangency. A tangent line may cross the graph in special cases however we would only be interested in the point of tangency.