Question 469936
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Hi
Does every straight line have a slope that is defined? NO
Vertical line, for example x = 3 has an undefined slope.
Using the point-slope formula, {{{m =(y[2] - y[1])/(x[2] - x[1])}}}
As the x value does not change:  Slope is undefined.  CANNOT divide by zero.
{{{drawing(300,300,   -6, 6, -6, 6,  blue(line(3,6,3,-6))  , grid(1),
graph( 300, 300, -6, 6, -6, 6))}}}