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_Why_Slopes_&_More_Math_1995

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Mean Value Theorem

Theorem G.2. [Mean Value Theorem] Assume f(x) is
continuous on an interval [a,b] and differentiable when a < x < b. Then there exists a point c interior to the interval [a,b] which satisfies
f¢(c) = f(b)-f(a)
b-a
Proof of Mean Value Theorem.

Let
G(x) = f(x)- f(b)-f(a)
b-a
·(x-a)
Then G(a) = f(a) and
G(x) = f(b)- f(b)-f(a)
b-a
·(b-a) = f(b)-(f(b)-f(a)) = f(a)
as well. Therefore by Rolle's theorem applied to the function G(x) on the interval [a,b], there exist a point c interior to the interval [a,b] such that 0 = G¢(c). But
G¢(x) = f¢(x)- f(b)-f(a)
b-a
With this, 0 = G¢(c) implies
f¢(c) = f(b)-f(a)
b-a

Remark.   If g(x) is continuous on an interval [a,b] then the mean value of the g(x) on the interval is the unique number r = [1/(b-a)]òab g(x)  dx. It is the unique number with the property that 0 = òab [g(x)-r]  dx. Now if g(x) = f¢(x) is the slope or derivative of a function then the mean-value of the slope g(x) = f¢(x) on the interval [a,b] is r = [(f(b)-f(a))/(b-a)]. This may explain the phrase Mean Value employed above.

 

the Real Analysis appendices of
Why Slopes
and
More Math

understanding & explaining
Reason and Math
Volume 3
Printed in Canada
ISBN 0-9697564-3-7

Presenting Appendices from  Volume 3, Why Slopes and More Math,  If the  epsilon-delta viewpoint of limits, continuity and convergence is not yet comfortable, see  Chapters 14 to 19 in Volume 3 are related.  

A. What's Next
B. Pigeon Hole Principle
B. Bolzano-Weierstrass
C1. Triangle Inequality
C2. Triangle Inequality
C. More T.Inequality
D. Sets & Sequences
D. Monotone Sequences
E. Limits,  Properties
E Limits & Error Control
F. Continuous Functions
F. Closed Range Thm
F. Intermediate Val. Thm
F. Compactness Thm
F. Equicontinuity Thm
F Extreme Value Thm
G. Rolle's Theorem etc
G. Mean Val. Thm.
G. Constant Difference Thm
G. Lipschitz Continuity I
PS: One Sided Range Theorems
G. Velocity Revisited
G. Sufficient Conditions
H. Riemann Sums Conv
H. Lipschitz Continuity II

Proofs of  one-sided theorems could be of interest in the study of 2D topology.


If  you like these appendices to Volume 3,  you may also like (a)  the foreword of Volume 3 and chapter 14 with its decimal view of limits, (b) Volume 2,  Three Skills for Algebra (for its 4 skills, not 3, for algebra), (c)  this treatment of  Exponents & Radicals Exactly,  (d) this geometric treatment of  complex numbers,  (e) the  Euclidean Geometry with a geometric proof of the distributive law for complex numbers,   (f) Pattern Based Reason  - its  logic elements and  online postscripts for 

Vol 1A Logic Postscripts
online only include

Proof by Absurdity alias proof by contradiction

How the demand for consistency supports the law of the excluded middle

Reality versus or with the aid of Imagination

 


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