Question 400179
if A(x1,y1) B(x2,y2)then midpoint M(x,y)formula
{{{x=(x1+x2)/2}}}  {{{y=(y1+y2)/2}}} 
In text A(0,-4) midpoint is (0,-2), put in formula 
for x ...{{{x=(x1+x2)/2}}}
{{{0=(0+x2)/2}}} 
{{{(0+x2)=0}}} 
{{{x2=0}}}
for y ...{{{y=(y1+y2)/2}}} 
{{{-2=(-4+y2)/2}}} 
{{{-4+y2=-2*2}}} 
{{{y2=-4+4}}} 
{{{y2=0}}}
B(0,0)