
William W. answered 08/01/23
Experienced Tutor and Retired Engineer
I believe the key is in the direction to "estimate" to value of "c". Draw a line (with slope -1/2) that goes between (2, 3) and (6, 1). Draw a series of parallel lines and look for one (or more) that is/are tangent to the function curve. Draw the tangent point(s). The approximate x-value of the tangent point(s) is/are the value(s) of "c".
This example shows three values of "c":