Question

M is the midpoint of segment CD. Given M(-2,2) and C(2,8), find the coordinates of D.

Answer 1

`~~~~~~~~~~~~\textit{middle point of 2 points } \\\\ C(\stackrel{x_1}{2}~,~\stackrel{y_1}{8})\qquad D(\stackrel{x_2}{x}~,~\stackrel{y_2}{y}) \qquad \left(\cfrac{ x_2 + x_1}{2}~~~ ,~~~ \cfrac{ y_2 + y_1}{2} \right) \\\\\\ \left(\cfrac{ x + 2}{2}~~~ ,~~~ \cfrac{ y + 8}{2} \right)~~ = ~~\stackrel{\stackrel{M}{\downarrow }}{(-2~~,~~2)}\implies \begin{cases} \cfrac{x+2}{2}=-2\\[1em] x+2=-4\\ \boxed{x=-6}\\[-0.5em] \hrulefill\\ \cfrac{y+8}{2}=2\\[1em] y+8=4\\ \boxed{y=-4} \end{cases}`