#color(red)(S)color(blue)(R)# is a line segment with #color(blue)(R)# at #color(blue)("("9,7")")# and the midpoint of #color(red(S)color(blue)(R)# (let's call it #color(green)(T)#) at #color(green)("("5,4")")#
Let the coordinates of #color(red)(S)# be #color(red)("("x_s,y_s")")#
Since #color(green)(T)# is the midpoint of #color(red)(S)color(blue)(R)#
#(y " at "color(blue)(R)) - (y " at "color(green)(T)) =(y " at " color(green)(T)) - (y " at " color(red)(S))#
That is
#color(blue)(7)-color(green)(4) = color(green)(4)-color(red)(y_s)#
#rarr color(red)(y_s) =1#
Similarly for #color(red)(x_s)#
#color(blue)(9)-color(green)(5) = color(green)(5)-color(red)(x_s)#
#rarr color(red)(x_s)=1#
The coordinates of #color(red)(S)# are #color(red)("("1,1")")#
