Unit #9 : Definite Integral Properties, Fundamental Theorem of Calculus

Transcription

1 Unit #9 : Definite Integrl Properties, Fundmentl Theorem of Clculus Gols: Identify properties of definite integrls Define odd nd even functions, nd reltionship to integrl vlues Introduce the Fundmentl Theorem of Clculus Compute simple nti-derivtives nd definite integrls Reding: Textbook reding for Unit #9 : Study Sections 5.4, 5.3, 6.2

2 Definite Integrls in Modeling - 1 Definite Integrls in Modeling One of the primry pplictions of integrtion is to use known rte of chnge, nd compute the net chnge over some time intervl. Exmple: Suppose wter is flowing into/out of tnk t rte given by r(t) = t L/min, where positive vlues indicte the flow is into the tnk. Write n integrl tht expresses the chnge in the volume of wter in the tnk during the first 30 minutes of filling.

3 Definite Integrls in Modeling - 2 Estimte the integrl using left-hnd rule with three intervls. Does this informtion tell you the ctul volume in the tnk fter 30 minutes? Why or why not?

4 Definite Integrls in Modeling - 3 Question: If h(t) represents the height of child (in cm) t time t (in yers), nd the child is 120 cm tll t ge 10, how would you represent the mount the child grew between t = 10 nd t = 18 yers? A. B. C. D h(t) dt h(t) dt h (t) dt h (t) dt + 120

5 Limit Properties for Integrls - 1 Properties of Definite Integrls Exmple: Sketch the re implicit in the integrl π/3 π/3 cos(x) dx If you were told tht sketched. π/3 0 cos(x) dx = 3, find the size of the re you 2

6 Limit Properties for Integrls - 2 This exmple highlights n importnt nd intuitive generl property of definite integrls. Additive Intervl Property of Definite Integrls f(x) dx = c f(x) dx + c f(x) dx Explin this generl property in words nd with digrm.

7 Limit Properties for Integrls - 3 A more rrely helpful, but eqully true, corollry of this property is second property: Reversed Intervl Property of Definite Integrls Use the integrl π/3 0 cos(x) dx + f(x) dx = 0 π/3 cos(x)dx, nd the erlier intervl property, to illustrte the reversed intervl property. b f(x) dx

8 Limit Properties for Integrls - 4 Give rtionle relted to Riemnn sums for the Reversed Intervl property.

9 Integrls of Even nd Odd Functions - 1 Even nd Odd Functions These properties cn be helpful especilly when deling with even nd odd functions. Define n even function. Give some exmples nd sketch them.

10 Define n odd function. Give some exmples nd sketch them. Integrls of Even nd Odd Functions - 2

11 Integrls of Even nd Odd Functions - 3 Integrl Properties of Even nd Odd Functions Find property of odd functions when you integrte on both sides of x = 0.

12 Integrls of Even nd Odd Functions - 4 Find property of even functions when you integrte on both sides of x = 0.

13 Scling, Adding Definite Integrls - 1 Linerity of Definite Integrls Exmple: If f(x) dx = 10, then wht is the vlue of Sketch n re rtionle for this reltion. 5f(x) dx?

14 Scling, Adding Definite Integrls - 2 Exmple: If f(x) dx = 2, nd g(x) dx = 4 then wht is the vlue of f(x) + g(x) dx? Agin, sketch n re rtionle for this reltion.

15 Scling, Adding Definite Integrls - 3 Linerity of Definite Integrls kf(x) dx = k f(x) ± g(x) dx = f(x) dx f(x) dx ± g(x) dx

16 Bounds on Integrls - 1 Simple Bounds on Definite Integrls Exmple: Sketch grph of f(x) = 5 sin(2πx), then use it to mke n re rgument proving the sttement tht sin (2πx) dx 5 2

17 Bounds on Integrls - 2 Simple Mximum nd Minimum Vlues for Definite Integrls If function f(x) is continuous nd bounded between y = m nd y = M on the intervl [, b], i.e. m f(x) M on the intervl, then m(b ) f(x) dx M(b ) Note tht the mximum nd minimum vlues we get with the method bove re quite crude. Sometimes you will be sked for much more precise vlues which cn often be just s esy to find. Exmple: Use the grph to find the exct vlue of just rnge, but the single correct re vlue sin(2πx) dx i.e. not

18 Bounds on Integrls - 3 Reltive Sizes of Definite Integrls Exmple: Two crs strt t the sme time from the sme strting point. For the first second, the first cr moves t velocity v 1 = t, nd the second cr moves t velocity v 2 = t 2. Sketch both velocities over the relevnt intervl.

19 Bounds on Integrls - 4 Which cr trvels further in the first second? Relte this to definite integrl. Comprison of Definite Integrls If f(x) g(x) on n intervl [, b], then f(x) dx g(x) dx

20 The Fundmentl Theorem of Clculus - Theory - 1 The Fundmentl Theorem of Clculus Reding: Section 5.3 nd 6.2 We hve now drwn firm reltionship between re clcultions (nd physicl properties tht cn be tied to n re clcultion on grph). The time hs now come to build method to compute these res in systemtic wy. The Fundmentl Theorem of Clculus If f is continuous on the intervl [, b], nd we define relted function F (x) such tht F (x) = f(x), then f(x) dx = F (b) F ()

21 The Fundmentl Theorem of Clculus - Theory - 2 The fundmentl theorem ties the re clcultion of definite integrl bck to our erlier slope clcultions from derivtives. However, it chnges the direction in which we tke the derivtive: Given f(x), we find the slope by finding the derivtive of f(x), or f (x). Given f(x), we find the re f(x) dx by finding F (x) which is the ntiderivtive of f(x); i.e. function F (x) for which F (x) = f(x).

22 The Fundmentl Theorem of Clculus - Theory - 3 In other words, if we cn find n nti-derivtive F (x), then clculting the vlue of the definite integrl requires simple evlution of F (x) t two points (F (b) F ()). This lst step is much esier thn computing n re using finite Riemnn sums, nd lso provides n exct vlue of the integrl insted of n estimte.

23 The Fundmentl Theorem of Clculus - Exmple - 1 Exmple: Use the Fundmentl Theorem of Clculus to find the re bounded ( by ) the x-xis, the line x = 2, nd the grph y = x 2. Use the fct tht d 1 dx 3 x3 = x 2.

24 The Fundmentl Theorem of Clculus - Exmple - 2 We used the fct tht F (x) = 1 3 x3 is n nti-derivtive of x 2, so we were ble use the Fundmentl Theorem. Give nother function F (x) which would lso stisfy d dx F (x) = x2. Use the Fundmentl Theorem gin with this new function to find the re implied by 2 0 x 2 dx.

25 The Fundmentl Theorem of Clculus - Exmple - 3 Did the re/definite integrl vlue chnge? Why or why not? Bsed on tht result, give the most generl version of F (x) you cn think of. d Confirm tht dx F (x) = x2.

26 Bsic Anti-Derivtives - Reference - 1 With our extensive prctice with derivtives erlier, we should find it strightforwrd to determine some simple nti-derivtives. Complete the following tble of nti-derivtives. function f(x) nti-derivtive F(x) x 2 x C x n x 2 + 3x 2

27 Bsic Anti-Derivtives - Reference - 2 function f(x) nti-derivtive F(x) cos x sin x x + sin x

28 Bsic Anti-Derivtives - Reference - 3 function f(x) nti-derivtive F(x) e x 2 x 1 1 x x 2 1 x

29 Bsic Anti-Derivtives - Reference - 4 The chief importnce of the Fundmentl Theorem of Clculus (F.T.C.) is tht it enbles us (potentilly t lest) to find vlues of definite integrls more ccurtely nd more simply thn by the method of clculting Riemnn sums. In principle, the F.T.C. gives precise nswer to the integrl, while clculting (finite) Riemnn sum gives you no better thn n pproximtion.

30 Bsic Anti-Derivtives - Exmples - 1 Exmple: Consider the re of the tringle bounded by y = 4x, x = 0 nd x = 4. Compute the re bsed on sketch, nd then by constructing n integrl nd using nti-derivtives to compute its vlue.

31 Bsic Anti-Derivtives - Exmples - 2 Exmple: Use definite integrl nd nti-derivtives to compute the re under the prbol y = 6x 2 between x = 0 nd x = 5.

32 Bsic Anti-Derivtives - 1/x - 1 The lst entry in our nti-derivtive tble ws f(x) = 1. It is bit of specil x cse, s we cn see in the following exmple. 1 1 Exmple: Sketch the re implied by the integrl x dx. 3

33 Bsic Anti-Derivtives - 1/x - 2 Exmple: Now use the nti-derivtive nd the Fundmentl Theorem of Clculus to obtin the exct re under f(x) = 1 between x = 3 nd x = 1. x Mke ny necessry dpttions to our erlier nti-derivtive tble.

34 Bsic Anti-Derivtives - 1/x - 3

35 Definite vs. Indefinite Integrls - 1 Anti-derivtives nd the Fundmentl Theorem of Clculus The F.T.C. tells us tht if we wnt to evlute f(x) dx ll we need to do is find n nti-derivtive F (x) of f(x) nd then evlute F (b) F (). THERE IS A CATCH. While in mny cses this relly is very clever nd strightforwrd, in other cses finding the nti-derivtive cn be surprisingly difficult. This week, we will stick with simple nti-derivtives; in lter weeks we will develop techniques to find more complicted nti-derivtives. Some generl remrks t this point will be helpful.

36 Definite vs. Indefinite Integrls - 2 Remrk 1 Becuse of the importnce of finding n nti-derivtive of f(x) when you wnt to clculte f(x) dx, it hs become customry to denote the nti-derivtive itself by the symbol f(x) dx The symbol f(x) dx (with no limits on the integrl) refers to the nti-derivtive(s) of f(x), nd is clled the indefinite integrl of f(x) Note tht the definite integrl is number, but the indefinite integrl is function (relly fmily of functions).

37 Definite vs. Indefinite Integrls - 3 Remrk 2 Since there re lwys infinitely mny nti-derivtives, ll differing from ech other by constnt, we customrily write the nti-derivtive s fmily of functions, in the form F (x) + C. For exmple, x 2 dx = x3 3 + C Note tht n nti-derivtive is single function, while the indefinite integrl is fmily of functions.

38 Definite vs. Indefinite Integrls - 4 Remrk 3 Since the lst step in the evlution of the integrl f(x) dx, once the ntiderivtive F (x) is found, is the evlution F (b) F (), it is customry to write F (x) b in plce of F (b) F (), s in 4 x 2 dx = x3 4 3 = Remrk 4 The vrible x in the definite integrl 0 0 f(x) dx is clled the vrible of integrtion. It cn be replced by nother vrible nme without ltering the vlue of the integrl. f(x) dx = f(u) du = f(θ) dθ