If C(3,6) is the midpoint of the line interval AB and A has Coordinates(-1,1) find the coordinates of B.

Let the coordinates of B be

 $\left(x_1,y_1\right)$

The formula is

  $\left(\frac{x_1+x_2}{2},\frac{y_1+y_2}{2}\right)$

$\frac{x_1+\left(-1\right)}{2}=3$

and

  $\frac{y_1+1}{2}=6$

$x_1-1=6$$y_1=11$

and

$y_1+1=12$

So

 $x_1=7$

and

$y_1=11$

Thus, B has Coordinate $(7,11).$