Point J has an x coordinate of x = a Point G has a y coordinate of y = a So point H has the coordinates (x,y) = (a,a) We simply move straight up from point J to get to H. At the same time, we move horizontally across to go from G to H. This is why H has half the coordinates from each J and G
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As for the slope of GJ, we use the slope formula m = (y2-y1)/(x2-x1) m = (0-a)/(a-0) m = -a/a m = -1 So that shows why the slope of GJ is -1
Multiplying the slope of KH (1) and the slope of GJ (-1), we get 1 times -1 = -1 The product being -1 shows the diagonals KH and GJ are perpendicular. They form a 90 degree angle.
