An interesting property of a cubic function with 3 x-intercepts: a tangent line at the average of two intercepts passes through the third.
Turn on the axes and sketch a cubic which crosses the x-axis 3 times.
Enter its equation as k*(x-a)*(x-b)*(x-c)
Place a point on the curve and set its location to be (a+b)/2
Create the tangent at this point
Construct the intersection between the tangent and the x-axis.
Use the Symbolic Panel to get the coordinates of point B.
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