Question 186626
First, find the eqaution of the line defined by the two given points
*[invoke find_equation_of_line 1, 2, -3, 8]

Now that that equation, plug in x=5 and solve for y
{{{y=(-1.5)x + (3.5)}}}
{{{y=(-1.5)5 + (3.5)}}}
{{{y = -7.5 + 3.5}}}
{{{y = -4}}}

Look at the line, is the point (5,-4) on it?