coordinates : A(1,2) B(-5,6) C(7,-4) D(-2,t) - All are taken in order
gradient of AB = (6-2)/(-5-1) = 4/-6 = -⅔
since it is quadrilateral, AB//CD
gradient of CD = -⅔
equation of CD : y-(-4)=-⅔(x-7)
y+4=-⅔x+14/3
y=-⅔x+⅔
now, sub x=-2 from D(-2,t)
since t is the y-coordinate of point D
t=-⅔(-2)+⅔
t=2
Therefore, t=2
