# The Fundamental Theorem of Calculus and Mean

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The Fundamental Theorem of Calculus and Mean Value Theorem 2
We’ve learned two different branches of calculus so far:
differentiation and integration. Finding slopes of tangent lines and
finding areas under curves seem unrelated, but in fact, they are very
closely related. It was Isaac Newton’s teacher at Cambridge
University, a man name Isaac Barrow (1630 – 1677), who
discovered that these two processes are actually inverse operations
of each other in much the same way division and multiplication are.
It was Newton and Leibniz who exploited this idea and developed the
calculus into its current form.
The Theorem Barrow discovered that states this inverse relation
between differentiation and integration is called
The Fundamental Theorem of Calculus.
FToC1 bridges the antiderivative concept with the area problem.
This result, while taught early in elementary calculus courses, is actually a very deep result connecting
the purely algebraic indefinite integral and the purely analytic (or geometric) definite integral.
To evaluate an integral, take the antiderivatives and subtract.
It can be proved and the proof can be found elsewhere (WEB)
It is a “shortcut” rule for integration: an easier way (from Riemann sums and other methods) to calculate
definite integrals.
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π
π­π»ππͺ π
∫ π(π) ππ = π­(π) − π­(π)
π
3
4
π
π­π»ππͺ π (ππππ π)
π­(π) = ∫ π(π) ππ
πππππ ππππππππ ππ π
π
where π is a continuous function on [π, π], and π₯ varies between π and π. Notice that this integral equation
is a function of π₯, which appears as the upper limit of integration. If π(π‘) happens to be positive, and we
let π₯ π (π, π] , then we can define πΉ(π₯) as the area under the curve from π to π₯.
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π₯
πΉ(π₯) = ∫(π‘ 2 + π‘ + 1) = (
3
π₯
π‘3 π‘2
π₯3 π₯2
33
+ + π‘)| =
+ +π₯−
3
2
3
2
2
3
π π₯3 π₯2
33
( + + π₯ − ) = π₯2 + π₯ + 1
ππ₯ 3
2
2
π
π­π»ππͺ π (ππππ π)
π­(π) = ∫ π(π) ππ
π≤π≤π
π
π΄ππππ‘πππππππ¦ ππ‘ ππ  ππ πππππππππ‘π πππ‘πππππ ππ π(π₯) [πΉ ′ (π₯) = π(π₯) ], π‘βππ‘ ππ
π
π­π»ππͺ π (ππππ π)
π
π­′ (π) =
∫ π(π)ππ = π(π)
ππ
π
1. Derivative of an integral
2. Derivative matches upper limit of integration
3. Lower limit of integration is a constant.
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π­π»ππͺ π ,
ππππ πππππππ ππππ
π(π)
π
[ ∫ π(π)ππ = π[π(π)] β π′ (π) − π[π(π)] β π′(π)]
ππ
π(π)
Example 10:
Evaluate the following using the FTOC2, then if feeling bored verify by doing in the
Loooooooong way.
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For a positive function π(π₯), there exists at least one number π ≤ π ≤ π
such that the rectangle with base [π, π] and height π(π) has the same
area as the region under the graph of π(π₯) from π to π.
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Sometimes we might have to solve an integral equation! Being able to simplify definite integrals with
variables in the interval of integration is important. Here are a couple of examples showing an important
application that is important.
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In the previous example, the first method relied heavily upon our ability to find the antiderivative of the
integrand. This is not always easy, possible, or prudent! Being able to express a particular value of a
particular solution to a derivative as a definite integral is of paramount importance, especially when we
don’t know how to find a general antiderivative. (calculator can do easily definite integrals – see
problem 20)
Hard Facts To Refute:
A. Where you are at any given time is a function of 1) where you started and 2) where you’ve gone from
B. What you have at any given moment is a function of 1) what you started with plus 2) what you’ve
accumulated since then.
When you accumulate at a variable rate, you can to use the definite integral to find your net
accumulation.
Important Idea of Accumulation********************************(* means VERY IMPORTANT)
What one has now = What one started with + What one has accumulated since one started
This can be expressed mathematically as
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SOLUTIONS
12
ππ‘
∫0 [50 + 14π ππ (12)] ππ‘
1
12
ππ‘ 12
14
π΄π£π π£πππ’π =
=
≈ 58.913
[50π‘ − 14 πππ  ( )]| = 50 + 2
12 − 0
12
π
12 0
π
2
2
∫−1[1 + π₯ 2 ]ππ₯ 1
π₯3
1
8
1
π(π) =
= [π₯ + ]| = [2 + − (−1) − (− )] = 2
2 − (−1)
3
3 −1 3
3
3
1 + x2 = 2 βΉ π = &plusmn; 1
for x = &plusmn; 1
For positive function π(π₯) = 1 + π₯ 2 , there exist two numbers π = &plusmn;1 such that the rectangle with
base [−1, 1] and height π(&plusmn;1) has the same area as the region under the graph of π(π₯) from -1 to 2.
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The average rate of change of a car’s position over an interval is represented graphically as the slope of
the secant line to the graph position/time over the interval.
π£ππ£π =
π₯(π‘2 ) − π₯(π‘1 )
π‘2 − π‘1
Average value of velocity over the same interval is:
π‘2
π£ππ£π
1
=
∫ π£(π‘) ππ‘
π‘2 − π‘1
π‘1
π‘2
π‘2
1
1
1
[π₯(π‘2 ) − π₯(π‘1 )] ππ¦ πΉπππΆ 1
πππππ:
∫ π£(π‘) ππ‘ =
∫ π₯′(π‘) ππ‘ =
π‘2 − π‘1
π‘2 − π‘1
π‘2 − π‘1
π‘1
πππ£π =
π‘1
∑ π(π₯)
≈ 40.429
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Area
area = 1160
average=1160/30 ≈ 38.667
trapezoidal approximation is more accurate that LRAM (basically arithmetic mean)
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(π)
2
π(π₯) = ∫(2π₯ 2 − 2)ππ₯ = π₯ 3 − 2π₯ + πΆ
3
π(0) = 5
=πΆ
2
π(π₯) = 3 π₯ 3 − 2π₯ + 5
π(2) =
19
3
π₯
(π)
2
π(π₯) = π(0) + ∫ π ′ (π₯)ππ₯
π(2) = 5 + ∫(2π₯ 2 − 2)ππ₯ =
0
0
19
3
this one was easy to solve analytically
If it was not formula (d) should be
used with different x every time
calculator can easily calculate
numerically definite integrals.
Look at problem 20.
π₯
π₯
2
(π) π(π₯) = π(2) + ∫ 4π ππ (2π₯) ππ₯ = −2 + ∫ 4π ππ2 (2π₯) ππ₯
2
2
π₯
π₯
π(π₯) = π(2) + ∫ π′(π₯) ππ₯ = −π + ∫ π π ππ π₯ ππ₯
(π) π(2) = −π
2
2
π
0
(π) π(π) = −π + ∫ π π ππ π₯ ππ₯ ≈ −1.169
(π) π(π) = −π + ∫ π π ππ π₯ ππ₯ ≈ −7.378
2
2
π‘
π(π‘) = π(0) + ∫ π′(π‘) ππ‘
βΉ π(14) = 180 + π(π‘)|14
0
0
π(14) = 180 + 10 π ππ
7π
≈ 172.930
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ππ’ππππ πΆβπππ π‘πππ  π‘πππ? π€βπ ππππππ?