# Translations:Raypath for velocity linear with depth/18/en

Note that the vertical component does not depend on the angle . As a result, the family of rays with the given velocity function is made up of the origin and that have their centers on the line . The circular raypath starts at the origin (which is the shot point). The tangent to the circle at the shot point makes an angle with the positive *y*-axis.

Often, we will know only that the ray passes through a certain point, say, , and we must determine the equation of the ray. This problem can be solved as described here and shown in Figure 12. Draw line *OB*. The midpoint of this line is . The center of the raypath circle must lie on the perpendicular bisector of the line *OB*. The center of the raypath circle also must lie on the horizontal line through the point . The intersection of these two lines of determination gives the center *E* of the raypath circle. From the geometry, we see that