# slope at a point on a graph

• Jan 14th 2010, 10:22 AM
Juggalomike
slope at a point on a graph
ALright i am stuck on this question, a friend told me to simply draw a line at that point and figure the slope from that, however the answer im getting itsnt working, so heres the question

Using graphical methods, determine at x= 2.8 the value of the derivative of function F(x) plotted in the graph below.
http://img32.imageshack.us/img32/751...09atestnd2.gif

also as a side note, i placed this in the calc forum because the question mentions derivative, if this is the wrong place please let me know.
• Jan 14th 2010, 10:30 AM
Calculus26
If you draw the tangent line at x = 2.8 it would appear that line would be horizontal. What is the slope of a horizontal line?
• Jan 14th 2010, 10:46 AM
Juggalomike
0, and i tried that answer but its saying its incorrect, which is whats throwing me off
• Jan 14th 2010, 10:48 AM
Calculus26
Without a microscope I would be hard pressed to think differently.

What is the answer supposed to be?
• Jan 14th 2010, 10:51 AM
Juggalomike
thats the problem, i have no idea, the program wont show me the answer until i get it right
• Jan 14th 2010, 04:09 PM
redirthgin
The slope would not be zero because if you notice the major ticks, they count by two. Therefore the minor ticks count by .4, not .2, so the tangent line does have a slope. I have the same exact problem with the same x value and I cannot get it either.
• Jan 15th 2010, 07:52 AM
Calculus26
Just as a ballpark approximation the tangent line seems to contain the points (2.8,11) and (-4,-3)

as a crude approx f ' (2.8) = [11-(-3)]/[2.8 - (-4)] = 2.06 = 2 to the nearest whole number

I simply laid a straightedge along the graph and identified 2 pts