options: Use similar triangles to explain why the slope m is the same between any two distinct points on a non-vertical line in the coordinate plane; derive the equation y = mx for a line through the origin and the equation y = mx + b for a line intercepting the vertical axis at b.

Graph proportional relationships, interpreting the unit rate as the slope of the graph. Compare two different proportional relationships represented in different ways. For example, compare a distance-time graph to a distance-time equation to determine which of two moving objects has greater speed.
problem_activity: Samantha found the slope of the line that passed through the points
$${(2, 6)}$$
and
$${(-4, 8)}$$
. Her work is shown below.
$${{8-6\over {2-(-4)}} = {2\over 2+4 }= {2\over 6} = {1\over3}}$$
Samantha made an error in her work. Describe the error and then find the correct slope of the line through the two given points.


correct_option_index: 0