Answer
(-4,-8)
Work Step by Step
given mid point(2,1) point A(8,10)
To find point B(x2,y2)
M(xm,ym) = ($\frac{x1+x2}{2}$, $\frac{y1+y2}{2}$)
(2,1) = ($\frac{8+x2}{2}$ , $\frac{10 + y2}{2}$)
2 = $\frac{8+x2}{2}$ , 1= $\frac{10+y2}{2}$
x2=4-8 , y2 =2-10
x2=-4, y2=-8
B = (-4,-8)