[tex](-15,9) \\
x_1=-15 \\
y_1=9 \\ \\
(-4,11) \\
x_2=-4 \\
y_2=11 \\ \\
\hbox{the length:} \\
l=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}=\sqrt{(-4+15)^2+(11-9)^2}=\\
=\sqrt{11^2+2^2}=\sqrt{121+4}=\sqrt{125}=\sqrt{25 \times 5}=5\sqrt{5} \\ \\
\hbox{the midpoint:} (\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2}) \\
\frac{x_1+x_2}{2}=\frac{-15-4}{2}=\frac{-19}{2}=-9.5 \\
\frac{y_1+y_2}{2}=\frac{9+11}{2}=\frac{20}{2}=10 \\
(-9.5,10)[/tex]
The length of the segment is 5√5, the midpoint of the segment is (-9.5,10).
