Question 1112201
slope = [ change in y ] / [ change in x ]
( 9,-3 )
( 9, -9 )
{{{ m = ( -3 -(-9) ) / ( 9 - 9 ) }}}
{{{ m = 6/0 }}}
The zero in the denominator says that the
slope is infinite. 
Infinite slope means the line is vertical.