Answer
a) $12.$
b)$(4,2)$.
Work Step by Step
The distance formula from $P_1(x_1,y_1)$ to $P_2(x_2,y_2)$ is $d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}$.
The midpoint $M$ of the line segment from $P_1(x_1,y_1)$ to $P_2(x_2,y_2)$ is: $(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2})$.
Hence:
a) $d=\sqrt{(4-4)^2+(-4-8)^2}=\sqrt{0+144}=\sqrt{144}=12.$
b)$M=(\frac{4+4}{2},\frac{-4+8}{2})=(4,2)$.
