Resposta
Midpoint $M = \left(\frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2}\right)$. Distance $d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}$.
Explicação
The distance formula is a direct application of the Pythagorean Theorem $a^2 + b^2 = c^2$ in the Cartesian coordinate plane.