Question 840950
Midpoints are averages of x and y values.
{{{x[m]=(x[1]+x[2])/2=5}}}
{{{(9+x[2])/2=5}}}
{{{9+x[2]=10}}}
{{{x[2]=1}}}
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{{{y[m]=(y[1]+y[2])/2=-7}}}
{{{(-7+y[2])/2=-7}}}
{{{-7+y[2]=-14}}}
{{{y[2]=-7}}}
The other point is (1,-7).
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{{{drawing(300,300,-2,10,-10,2,grid(1),
circle(1,-7,0.2),
circle(5,-7,0.2),
circle(9,-7,0.2),
green(line(1,-7,9,-7)))}}}