Choose the points that you wish to convert. Determine the equation for the curve represented by those points, if it's not already given.
Calculate the coordinates of the points immediately before and after each point you wish to convert. The points should be as close to the specified point as possible to get the most accurate measurement of the tangent.
Subtract the coordinates of the preceding point from the coordinates of the following point. The resulting difference is the change in position from the preceding location to the following location. For example, if you were subtracting (3,4) from (4,6), you would get (1,2).
Divide the change in the “x” coordinate by the change in the “y” coordinate. This dividend represents the slope of the curve at the specified point, and the slope represents the tangential component at that point. Continuing the example above, divide 1 by 2 to get 0.5. The tangential coordinate for the midpoint between (3,4) and (4,6) is 0.5. Since the slope is also the trigonometric tangent of the angle formed by the line running through the two points and the x-axis, it can also be expressed in degrees or radians. A tangent of 0.5 would translate to about 27 degrees or 0.47 radians.
Calculate the inverse of the tangent and multiply by –1 to obtain the normal component. The normal component of the coordinates will always be perpendicular to the tangential component. In the example being used, the normal component of the coordinates is –2. This translates to either 116 degrees and 2.02 radians, or 296 degrees and 5.18 radians. The normal component will always be in the direction of the concave side of the curve.