In the xy-plane, the center of a circle has coordinates (3, -7). If one endpoint of a diameter of the circle is (-2, -7), what are the coordinates of the other endpoint of this diameter?
Let the co-ordinate of other endpoint be $\displaystyle (x_1, y_1)$
Since, diameter connects these two end-points, so the center is midpoint of these two endpoints.
According to mid point formula,
$\displaystyle (3, -7) = \left(\frac{-2+x_1}{2}, \frac{-7+y_1}{2} \right)$
$\displaystyle \Rightarrow x_1=8,\;\;y_1=-7$
Did you get it now???