Reflections, or mirror isometries, denoted by "F""c","v", where "c" is a point in the plane and "v" is a unit vector in R2. ("F" is for "flip".) have the effect of reflecting the point "p" in the line "L" that is perpendicular to "v" and that passes through "c". The line "L" is called the reflection axis or the associated mirror. To find a formula for "F""c","v", we first use the dot product to find the component "t" of "p" − "c" in the "v" direction,