Question 551420
For a point (P), reflection in the origin would mean walk to the origin, and then keep walking the same distance in the same direction, going from (x,y) to (-x,-y) to find reflected point P'. In other words, turn your plane 180 degrees around the origin to move P onto P'.
{{{drawing(300,300,-5,5,-5,5,
arrow(-5,0,5,0), arrow(0,-5,0,5),
locate(0,5,y),locate(4.5,0,x),
red(triangle(0,0,2,0,2,4)),
blue(triangle(0,0,-2,0,-2,-4)),
locate(2.1,4,P (x,y)), locate(-2,-4,"P' (-x,-y)")
)}}}