Question 878444
The midpoint is the average of the x values and the y values for points R and S.
{{{x[m]=(x[r]+x[s])/2}}}
{{{x[r]=2x[m]-x[s]}}}
Similarly for {{{y}}}
{{{y[m]=(y[r]+y[s])/2}}}
{{{y[r]=2y[m]-y[s]}}}