Given g(x) is the integral from a to x of f(t) dt, we were able to derive that g'(x) = 1/h integral from x to x+h of f(t) dt. By the extreme value theorem there exists a min m and max M on [x,x+h] such that f(u) = m and f(v) = M and f(u)h<= integral x to x+h f(t) dt <= f(v)h (by properties of integrals). Dividing by h we get f(u)<= (g(x+h)- g(x)) / h <= f(v) by substitution. Here is where I'm confused, the text says if we let h--> 0 then u --> x and v--> x since u and v lie in [x,x+h]. I'm not understanding how u--> x and v--> x.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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I'm self studying Stewart calculus and I'm working through the proof of FTC part 1. I'm stuck on a line in the proof that is preventing me from preceding.

Given g(x) is the integral from a to x of f(t) dt, we were able to derive that g'(x) = 1/h integral from x to x+h of f(t) dt.

By the extreme value theorem there exists a min m and max M on [x,x+h] such that f(u) = m and f(v) = M and f(u)h<= integral x to x+h f(t) dt <= f(v)h (by properties of integrals).

Dividing by h we get f(u)<= (g(x+h)- g(x)) / h <= f(v) by substitution.

Here is where I'm confused, the text says if we let h--> 0 then u --> x and v--> x since u and v lie in [x,x+h]. I'm not understanding how u--> x and v--> x. See 3rd image below, text is a red box. 

The Fundamental Theorem of Calculus, Part 1 If f is continuous on [a, b], then the
function g defined by
g(x) - S² (1) de a= x=b
is continuous on [a, b] and differentiable on (a, b), and g'(x)
Show Transcribed Text
2
that is,
g(x + h)
h
M.
Show Transcribed Text
3
g(x)
=
For now let's assume that h> 0. Since fis continuous on [x, x + h], the Extreme Value
Theorem says that there are numbers and in [x. x+h] such that f(u) m and
(v)M, where and M are the absolute minimum and maximum values of fon
[x, x + h]. (See Figure 6.)
By Property 8 of integrals, we have
Since h> 0, we can divide this inequality by h:
1 fath
mh=f(t) dt = Mh
S*** (1) dr
f(u) =
ATH
f(u)h = ™" f(t) dt = f(0)h
f(u) = = -1/2 √²+ h f(1) dt = f(v)
h
Now we use Equation 2 to replace the middle part of this inequality:
g(x + h) - g(x)
h
g
f(x).
= f(v)
Ĵ
Inequality 3 can be proved in a similar manner for the case where <0. (See Exercise 71.)
Now we let h→0. Then u→x and v→ x, since u and v lie between x and x + h.
Transcribed Image Text:The Fundamental Theorem of Calculus, Part 1 If f is continuous on [a, b], then the function g defined by g(x) - S² (1) de a= x=b is continuous on [a, b] and differentiable on (a, b), and g'(x) Show Transcribed Text 2 that is, g(x + h) h M. Show Transcribed Text 3 g(x) = For now let's assume that h> 0. Since fis continuous on [x, x + h], the Extreme Value Theorem says that there are numbers and in [x. x+h] such that f(u) m and (v)M, where and M are the absolute minimum and maximum values of fon [x, x + h]. (See Figure 6.) By Property 8 of integrals, we have Since h> 0, we can divide this inequality by h: 1 fath mh=f(t) dt = Mh S*** (1) dr f(u) = ATH f(u)h = ™" f(t) dt = f(0)h f(u) = = -1/2 √²+ h f(1) dt = f(v) h Now we use Equation 2 to replace the middle part of this inequality: g(x + h) - g(x) h g f(x). = f(v) Ĵ Inequality 3 can be proved in a similar manner for the case where <0. (See Exercise 71.) Now we let h→0. Then u→x and v→ x, since u and v lie between x and x + h.
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