Two curves touch each other if the angle between the tangents to the curves at the point of intersection is 0o, in which case we will have, tan?1 = tan?2. how is that possible? give an example?

let f(x) and g(x) be the two curves. At the point of contact df(x)/dx =dg(x)/dx, example consider the curves f(x)=y=x² and     g(x) =y=-x², at the point x=y=zero f'(x)=2x = g'(x)=-2x =0,and the common tangent is the x-axis