Question 156774
For the line segment AB, with A({{{x[1]}}},{{{y[1]}}}), B({{{x[2]}}},{{{y[2]}}}),
its midpoint is E({{{x[3]}}},{{{y[3]}}})
where 
{{{x[3]}}} = ({{{x[1]}}}+{{{x[2]}}})/2, 
{{{y[3]}}} = ({{{y[1]}}}+{{{y[2]}}})/2
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suppose the coordinates of point D is (x, y)
As E(0, 1) is the midpoint of CD, we have
{{{0 = (-3+x)/2}}}
{{{1 = (4+y)/2}}}
Solving the equations for x and y, we have
x = 3
y = -2
So the coordinates of point D is (3, -2)