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E1 - Antiderivatives and Indefinite Integrals IB Math HL/SL.

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1 E1 - Antiderivatives and Indefinite Integrals IB Math HL/SL

2 (A) Review - Simple Antiderivatives If v(t) = t 4 – 6t 2 + 4, find d(t) So we need to “undifferentiate” or “antidifferentiate” 3 functions (t 4, 6t 2, 3) So what equation did we differentiate to get t 4  recalling the power rule, it must have been a t 5 expression  but the derivative of t 5 is actually 5t 4  so if we have only t 4 as our “derivative”, then we are “off” by 1/5  so our “antiderivative” must be 1/5t 5 (test by differentiating  which does in fact give us 1t 4 ) Likewise, to have 6t 2 as a derivative, we must have started with a t 3 function  but which one?  if we differentiate t 3, we get 3t 2, so seeing that we have a 6t 2, we clearly have twice what we need  so we must have started with 2t 3 or one-third of 6t 3 (test by differentiating  which does in fact give us 6t 2 ) And then consider the 4 (or 4x 0 )  we must have started with an x 1 function  but which one?  if we differentiate x 1, then we get 1x 0  we have 4x 0, so we have four times what we need  so we must have started with 4x 1 or simply 4x (test by differentiating  which does in fact give us 3) So we have simply looked at power functions and seen a method for “undoing” a power rule  add one to the exponent, then adjust the coefficient by dividing by the new exponent

3 (B) Review - Simple Antiderivatives & Initial Conditions Another point needs to be addressed  so let’s work with an easier function Say v(t) = 4t (or rather d`(t) = 4t)  then what is d(t)?? If we anti-differentiate, we would predict d(t) = 2t 2, but we need to realize that there is more to it than that  Why?  lets consider some derivatives and some graphs

4 (B) Review - Simple Antiderivatives & Initial Conditions So our derivative of y` = 4x could have come from any of the three “antiderivatives” of y = 2x 2 or y = 2x or y = 2x 2 – 6 or any other combination of y = 2x 2 + C, where C is simply a constant that changes the y-intercept of the original parabola 2x 2 So our derivative of y` = 4x could have come from any of the three “antiderivatives” of y = 2x 2 or y = 2x or y = 2x 2 – 6 or any other combination of y = 2x 2 + C, where C is simply a constant that changes the y-intercept of the original parabola 2x 2

5 (B) Review - Simple Antiderivatives & Initial Conditions So back to our original problem  if v(t) = t 4 – 6t 2 + 4, find d(t) We have worked out that d(t) = 1/5t 5 – 2t 3 + 4t Having just seen the last graphic discussion about “families of curves”, we realize that we need to add some constant to the “antiderivative” equation (the distance equation) so our equation for d(t) becomes d(t) = 1/5t 5 – 2t 3 + 4t + C  which we will call our most general solution Now, if we knew some information about the distance function, we could solve for C and complete our equation  say at t = 0 sec, then d(0) = 2 m (the initial position of the object was 2 meters beyond some reference point) Now d(0) = 1/5(0) 5 – 2(0) 3 + 4(0) + C = 2  C = 2 Thus d(t) = 1/5t 5 – 2t 3 + 4t + 2 is our final specific solution

6 (C) Review - Common Antiderivatives The functions: dy/dx = x n dy/dx = 0 dy/dx = 1 dy/dx = 1/x dy/dx = e kx dy/dx = coskx dy/dx = sinkx The antiderivatives: y = x n+1 / (n+1) + C y = 1 y = x + C y = ln|x| + C y = 1/k e kx + C y = 1/k sin(kx) + C y = -1/k cos(kx) + C

7 (D) Indefinite Integrals - Definitions We have worked with motion applications and velocity functions  so we recognize that v(t) = s`(t) (i.e. that the velocity equation is simply the derivative of the position/displacement equation We have worked with motion applications and velocity functions  so we recognize that v(t) = s`(t) (i.e. that the velocity equation is simply the derivative of the position/displacement equation So we will generalize the anti-derivative idea by saying that the function we are trying to anti-differentiate simply represents a derivative equation (i.e. the velocity function is the derivative of the displacement function) So we will generalize the anti-derivative idea by saying that the function we are trying to anti-differentiate simply represents a derivative equation (i.e. the velocity function is the derivative of the displacement function) Definitions: an anti-derivative of f(x) is any function F(x) such that F`(x) = f(x)  If F(x) is any anti-derivative of f(x) then the most general anti-derivative of f(x) is called an indefinite integral and denoted  f(x)dx = F(x) + C where C is any constant Definitions: an anti-derivative of f(x) is any function F(x) such that F`(x) = f(x)  If F(x) is any anti-derivative of f(x) then the most general anti-derivative of f(x) is called an indefinite integral and denoted  f(x)dx = F(x) + C where C is any constant In this definition the  is called the integral symbol, f(x) is called the integrand, x is called the integration variable and the “C” is called the constant of integration In this definition the  is called the integral symbol, f(x) is called the integrand, x is called the integration variable and the “C” is called the constant of integration The process of finding an indefinite integral (or simply an integral) is called integration The process of finding an indefinite integral (or simply an integral) is called integration

8 (E) Properties of Indefinite Integrals  [c  f(x)]dx = c   f(x)dx  [c  f(x)]dx = c   f(x)dx  -f(x)dx = -  f(x)dx  -f(x)dx = -  f(x)dx  [f(x) + g(x)]dx =  f(x)dx +  g(x)dx  [f(x) + g(x)]dx =  f(x)dx +  g(x)dx which is similar to rules we have seen for derivatives which is similar to rules we have seen for derivatives And two other interesting “properties” need to be highlighted: And two other interesting “properties” need to be highlighted:  g`(x)dx = g(x) + C  g`(x)dx = g(x) + C d/dx  f(x)dx = f(x) d/dx  f(x)dx = f(x)

9 (F) Examples  (x 4 + 3x – 9)dx =  x 4 dx + 3  xdx - 9  dx  (x 4 + 3x – 9)dx =  x 4 dx + 3  xdx - 9  dx  (x 4 + 3x – 9)dx = 1/5 x5 + 3/2 x 2 – 9x + C  (x 4 + 3x – 9)dx = 1/5 x5 + 3/2 x 2 – 9x + C  e 2x dx =  e 2x dx =  sin(2x)dx =  sin(2x)dx =  (x 2  x)dx =  (x 2  x)dx =  (cos  + 2sin3  )d  =  (cos  + 2sin3  )d  =  (8x + sec 2 x)dx =  (8x + sec 2 x)dx =  (2 -  x) 2 dx =  (2 -  x) 2 dx = Continue now with these questions on line Continue now with these questions on line Problems & Solutions with Antiderivatives / Indefinite Integrals from Visual Calculus Problems & Solutions with Antiderivatives / Indefinite Integrals from Visual Calculus Problems & Solutions with Antiderivatives / Indefinite Integrals from Visual Calculus Problems & Solutions with Antiderivatives / Indefinite Integrals from Visual Calculus

10 (G) Indefinite Integrals with Initial Conditions Given that  f(x)dx = F(x) + C, we can determine a specific function if we knew what C was equal to  so if we knew something about the function F(x), then we could solve for C Given that  f(x)dx = F(x) + C, we can determine a specific function if we knew what C was equal to  so if we knew something about the function F(x), then we could solve for C Ex. Evaluate  (x 3 – 3x + 1)dx if F(0) = -2 Ex. Evaluate  (x 3 – 3x + 1)dx if F(0) = -2 F(x) =  x 3 dx - 3  xdx +  dx = ¼x 4 – 3/2x 2 + x + C F(x) =  x 3 dx - 3  xdx +  dx = ¼x 4 – 3/2x 2 + x + C Since F(0) = -2 = ¼(0) 4 – 3/2(0) 2 + (0) + C Since F(0) = -2 = ¼(0) 4 – 3/2(0) 2 + (0) + C So C = -2 and So C = -2 and F(x) = ¼x 4 – 3/2x 2 + x - 2 F(x) = ¼x 4 – 3/2x 2 + x - 2

11 (H) Examples – Indefinite Integrals with Initial Conditions Problems & Solutions with Antiderivatives / Indefinite Integrals and Initial Conditions from Visual Calculus Problems & Solutions with Antiderivatives / Indefinite Integrals and Initial Conditions from Visual Calculus Problems & Solutions with Antiderivatives / Indefinite Integrals and Initial Conditions from Visual Calculus Problems & Solutions with Antiderivatives / Indefinite Integrals and Initial Conditions from Visual Calculus Motion Problem #1 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #1 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #1 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #1 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #2 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #2 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #2 with Antiderivatives / Indefinite Integrals from Visual Calculus Motion Problem #2 with Antiderivatives / Indefinite Integrals from Visual Calculus

12 (I) Internet Links Calculus I (Math 2413) - Integrals from Paul Dawkins Calculus I (Math 2413) - Integrals from Paul Dawkins Calculus I (Math 2413) - Integrals from Paul Dawkins Calculus I (Math 2413) - Integrals from Paul Dawkins Tutorial: The Indefinite Integral from Stefan Waner's site "Everything for Calculus” Tutorial: The Indefinite Integral from Stefan Waner's site "Everything for Calculus” Tutorial: The Indefinite Integral from Stefan Waner's site "Everything for Calculus” Tutorial: The Indefinite Integral from Stefan Waner's site "Everything for Calculus” The Indefinite Integral from PK Ving's Problems & Solutions for Calculus 1 The Indefinite Integral from PK Ving's Problems & Solutions for Calculus 1 The Indefinite Integral from PK Ving's Problems & Solutions for Calculus 1 The Indefinite Integral from PK Ving's Problems & Solutions for Calculus 1 Karl's Calculus Tutor - Integration Using Your Rear View Mirror Karl's Calculus Tutor - Integration Using Your Rear View Mirror Karl's Calculus Tutor - Integration Using Your Rear View Mirror Karl's Calculus Tutor - Integration Using Your Rear View Mirror

13 (J) Homework Stewart, 1989, Chap 11.2, p505, Q1,2 Stewart, 1989, Chap 11.2, p505, Q1,2 Handout Handout


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