let's recall that in a Kite the diagonals meet each other at 90° angles, Check the picture below, so we're looking for the equation of a line that's perpendicular to BD and that passes through (-1 , 3).
keeping in mind that perpendicular lines have negative reciprocal slopes, let's check for the slope of BD
so we're really looking for the equation of a line whose slope is -1/3 and passes through point A
