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posted by  help_please_thanks on 3/21/2008 11:03:11 PM  |  status: Live  

which of the following is true abou the derivative?

Course Textbook Chapter Problem
Calculus N/A N/A N/A
Question Details:
 
(a) 
x 1.1 1.2 1.3 1.4
f(x) 4.18 4.38 4.56 4.73
Let f be a function such that f " (x) < 0 for all x in the closed interval [1,2] with selected values shown in the table above.  Which of the following must be true about f ' (1.2)?
 
 
               (a) f ' (1.2) < 0
               (b)  0 < f ' (1.2) < 1.6
               (c)  1.6 < f ' (1.2) < 1.8
               (d)  1.8 < f ' (1.2) < 2.0
               (e)  f ' (1.2) > 2.0
   ~ Kelly
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posted by jks777 on 3/21/2008 11:08:57 PM  |  status: Live
Asker's Rating: Lifesaver   
help_please_thanks's comment:
"thanks"
Response Details:
To find the slope of this problem, we should use the slope formula:
 
m = (y2 - y1)/(x2 - x1)
 
And then use the following combinations together: 1.1 to 1.2, 1.2 to 1.3 and 1.1 to 1.3 to determine how the slope is around 1.2
 
m = (f(1.2) - f(1.1))/(1.2 - 1.1)
m = (4.38 - 4.18)/(0.1) = .2/.1 = 2
 
m = (f(1.3) - f(1.2))/(1.3 - 1.2)
m = (4.56 - 4.38)/(0.1) = .2/.1 = 1.8
 
m = (f(1.3) - f(1.1))/(1.3 - 1.1)
m = (4.56 - 4.18)/(0.2) = .38/.2 = 1.9
 
This means the derivative will be between 1.8 < f'(1.2) < 2.0.  And that choice would be D.
Tags: Math, Calculus
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