Okay so in a problem I have a vector reflecting off a mirror. I have the equation for the normal of the mirror at the coordinates where the vector of light hits the mirror. The normal of the mirror and the vector incident are in the same geometric plane. How do I find the refection of the vector incident in this same plane. My vector incident is 5i + 10j + 10k some coordinates in plane are (5,0,0) angle between normal of mirror and vector incident is about 11.4 degrees The normal of the mirror is -i - j - k equation for plane -5y + 5z = 0 I think that's right. I have no idea how to find a new vector with this information.