Question 989546
The x-coordinate of the midpoint is at:
{{{ x[p] = ( x[1] + x[2] ) / 2 }}}
where {{{ x[1] }}} and {{{ x[2] }}} are 
x-coordinates of the endpoints
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The y-coordinate of the midpoint is at:
{{{ y[p] = ( y[1] + y[2] ) / 2 }}}
where {{{ y[1] }}} and {{{ y[2] }}} are 
y-coordinates of the endpoints
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I will say that:
( x[1], y[1] ) = M( 8, -2 )
( x[p], y[p] ) = P( -4, 6 )
I need to find N( x[2], y[2] )
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First, using:
{{{ x[p] = ( x[1] + x[2] ) / 2 }}}
{{{ -4 = ( 8 + x[2] ) / 2 }}}
{{{ -8 = 8 + x[2] }}}
{{{ x[2] = -16 }}}
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Next, using:
{{{ y[p] = ( y[1] + y[2] ) / 2 }}}
{{{ 6 = ( -2 + y[2] ) / 2 }}}
{{{ 12 = -2 + y[2] }}}
{{{ y[2] = 14 }}}
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The other endpoint is at: N( -16, 14 )
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check:
{{{ -4 = ( 8 + x[2] ) / 2 }}}
{{{ -4 = ( 8 +(-16) ) / 2 }}}
{{{ -4 = (-8)/2 }}}
{{{ -4 = -4 }}}
and
{{{ 6 = ( -2 + y[2] ) / 2 }}}
{{{ 6 = ( -2 + 14 ) / 2 }}}
{{{ 6 = 12/2 }}}
{{{ 6 = 6 }}}
OK