Answer :
[tex]A(x_A;\ y_A);\ B(x_B;\ y_B)\\\\midpoint\ AB:\left(\frac{x_A+x_B}{2};\ \frac{y_A+y_B}{2}\right)[/tex]
[tex]A(2;\ 9);\ B(x;\ y)\\\\midpoint\ AB:\left(\frac{11}{2};\ \frac{17}{2}\right)\\\\\frac{2+x}{2}=\frac{11}{2}\ and\ \frac{9+y}{2}=\frac{17}{2}\ \ \ \ \ |multiply\ both\ sides\ by\ 2\\\\2+x=11\ and\ 9+y=17\\\\x=11-2\ and\ y=17-9\\\\x=9\ and\ y=8\\\\Answer:endpoint\ (9;\ 8).[/tex]
[tex]A(2;\ 9);\ B(x;\ y)\\\\midpoint\ AB:\left(\frac{11}{2};\ \frac{17}{2}\right)\\\\\frac{2+x}{2}=\frac{11}{2}\ and\ \frac{9+y}{2}=\frac{17}{2}\ \ \ \ \ |multiply\ both\ sides\ by\ 2\\\\2+x=11\ and\ 9+y=17\\\\x=11-2\ and\ y=17-9\\\\x=9\ and\ y=8\\\\Answer:endpoint\ (9;\ 8).[/tex]
