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Lesson 60 — Term 6 Consolidation: Derivatives

Integrative workshop for Term 6: definition via limit, operational rules, chain rule, implicit derivative, higher derivatives, inverses, linearization, related rates, and differentiability.

Used in: 2nd Year HS — Term 6 · Equivalent Japanese Math III (Derivatives) · Equivalent German Analysis LK — Ableitung

f(x)=limh0f(x+h)f(x)hf'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}
Choose your door

Rigorous notation, full derivation, hypotheses

Formal Map of Term 6

Hierarchy of Differentiation Tools

"The derivative of a function ff at a value aa, denoted f(a)f'(a), is defined by the formula f(a)=limh0f(a+h)f(a)hf'(a) = \lim_{h\to 0}\frac{f(a+h)-f(a)}{h}, provided this limit exists." — Active Calculus, §1.3

Table of Fundamental Derivatives

f(x)f(x)f(x)f'(x)Rule
xnx^nnxn1n x^{n-1}Power
exe^xexe^xNatural Exponential
axa^xaxlnaa^x \ln aGeneral Exponential
lnx\ln x1/x1/xLogarithm
sinx\sin xcosx\cos xSine
cosx\cos xsinx-\sin xCosine
tanx\tan xsec2x\sec^2 xTangent
arcsinx\arcsin x1/1x21/\sqrt{1-x^2}Arcsine
arctanx\arctan x1/(1+x2)1/(1+x^2)Arctangent

Operational Rules

"The Product Rule states: if ff and gg are differentiable functions, then ddx[f(x)g(x)]=f(x)g(x)+f(x)g(x)\frac{d}{dx}[f(x)g(x)] = f'(x)g(x) + f(x)g'(x)." — OpenStax Calculus Vol. 1, §3.3

Implicit Derivative and Higher-Order Derivatives

Fundamental Theorem of Differentiability

"If ff is differentiable at aa, then ff is continuous at aa." — Active Calculus, §1.7

Pattern Recognition

Signal in Problem StatementTechnique
"Compute f(a)f'(a) directly"Rules + Table
"y=f(composite)y = f(\text{composite})"Chain Rule
"F(x,y)=0F(x, y) = 0, find yy'"Implicit Differentiation
"ff'', concavity, inflection points"Higher-Order Derivatives
"Derivative of arcsin\arcsin, arctan\arctan, ln\ln, exe^x, axa^x"Inverse Table
"Approximate f(x)f(x) near aa"Linearization
"How fast does XX change with time?"Related Rates
"ff is differentiable at aa?"Check continuity + two-sided limit

Solved Examples

Exercise list

50 exercises · 12 with worked solution (25%)

29 6 9 5 1
  1. Ex. 60.1

    Compute f(3)f'(3) using the definition of the derivative for f(x)=x2f(x) = x^2.

  2. Ex. 60.2

    Compute f(1)f'(1) using the definition for f(x)=1/xf(x) = 1/x.

  3. Ex. 60.3

    Compute f(4)f'(4) using the definition for f(x)=xf(x) = \sqrt{x}.

  4. Ex. 60.4

    What is f(a)f'(a) by the formal definition?

  5. Ex. 60.5

    Let g(x)=x2cos(1/x)g(x) = x^2 \cos(1/x) for x0x \neq 0 and g(0)=0g(0) = 0. Compute g(0)g'(0) using the definition.

  6. Ex. 60.6

    Compute f(x)f'(x) for f(x)=x43x2+7f(x) = x^4 - 3x^2 + 7.

  7. Ex. 60.7

    Compute h(x)h'(x) for h(x)=exsinxh(x) = e^x \sin x.

  8. Ex. 60.8

    Compute q(x)q'(x) for q(x)=x+1x1q(x) = \dfrac{x+1}{x-1}.

  9. Ex. 60.9Answer key

    Compute p(x)p'(x) for p(x)=xsinxp(x) = x \sin x.

  10. Ex. 60.10

    Compute r(x)r'(x) for r(x)=sinxx2r(x) = \dfrac{\sin x}{x^2} and simplify.

  11. Ex. 60.11

    Compute f(x)f'(x) for f(x)=x3exf(x) = x^3 e^x and factor the answer.

  12. Ex. 60.12Answer key

    Compute y(2)y'(2) for y(x)=x332x+1y(x) = \dfrac{x^3}{3} - 2x + 1.

  13. Ex. 60.13Answer key

    What is the correct formula for the derivative of the product u(x)v(x)u(x)\cdot v(x)?

  14. Ex. 60.14

    Compute f(x)f'(x) for f(x)=x2x21f(x) = \dfrac{x^2}{x^2 - 1}.

  15. Ex. 60.15Answer key

    Compute f(x)f'(x) for f(x)=(2x+1)5f(x) = (2x+1)^5.

  16. Ex. 60.16

    Compute g(x)g'(x) for g(x)=sin(x3)g(x) = \sin(x^3).

  17. Ex. 60.17

    Compute k(x)k'(x) for k(x)=ex2k(x) = e^{x^2}.

  18. Ex. 60.18

    Compute h(x)h'(x) for h(x)=ln(2x+3)h(x) = \ln(2x + 3).

  19. Ex. 60.19

    Compute m(x)m'(x) for m(x)=arcsin(x2)m(x) = \arcsin(x^2).

  20. Ex. 60.20

    Compute p(x)p'(x) for p(x)=cos(sinx)p(x) = \cos(\sin x).

  21. Ex. 60.21Answer key

    Compute f(x)f'(x) for f(x)=xxf(x) = x^x (x>0x > 0) using logarithmic differentiation.

  22. Ex. 60.22Answer key

    Compute w(x)w'(x) for w(x)=ln(sin(3x)+2)w(x) = \ln(\sin(3x) + 2).

  23. Ex. 60.23

    Compute yy' by implicit differentiation for x2+y2=25x^2 + y^2 = 25.

  24. Ex. 60.24

    Compute yy' at (1,1)(1, 1) for the curve x3+y3=2x^3 + y^3 = 2.

  25. Ex. 60.25Answer key

    Compute yy' at (0,π/2)(0, \pi/2) for sin(xy)=y\sin(xy) = y.

  26. Ex. 60.26

    Compute yy' for the ellipse x29+y24=1\dfrac{x^2}{9} + \dfrac{y^2}{4} = 1 and describe the tangent at (3,0)(3, 0).

  27. Ex. 60.27

    What does it mean to "treat yy as an implicit function of xx" when differentiating an equation?

  28. Ex. 60.28

    Compute yy'' implicitly for x2+y2=r2x^2 + y^2 = r^2.

  29. Ex. 60.29

    Compute yy' for x2y+xy2=6x^2 y + xy^2 = 6.

  30. Ex. 60.30

    Compute f(x)f''(x) for f(x)=x32x2+2x1f(x) = x^3 - 2x^2 + 2x - 1.

  31. Ex. 60.31

    Compute f(4)(x)f^{(4)}(x) for f(x)=sinxf(x) = \sin x.

  32. Ex. 60.32

    Compute f(x)f'(x) for f(x)=arctanxf(x) = \arctan x.

  33. Ex. 60.33Answer key

    Compute g(x)g'(x) for g(x)=arctan(2x)g(x) = \arctan(2x).

  34. Ex. 60.34

    Compute h(x)h'(x) for h(x)=ln(2x)h(x) = \ln(2x) and identify the most common error.

  35. Ex. 60.35Answer key

    Compute f(x)f'(x) for f(x)=axf(x) = a^x, with a>0a > 0 and a1a \neq 1.

  36. Ex. 60.36

    Compute f(50)(x)f^{(50)}(x) for f(x)=sin(2x)f(x) = \sin(2x).

  37. Ex. 60.37

    Use the linearization of f(x)=exf(x) = e^x at a=0a = 0 to approximate e0.1e^{0.1}.

  38. Ex. 60.38

    Use the linearization of f(x)=xf(x) = \sqrt{x} at a=25a = 25 to approximate 25.1\sqrt{25.1}.

  39. Ex. 60.39

    Use the linearization of f(x)=lnxf(x) = \ln x at a=1a = 1 to approximate ln(1.05)\ln(1.05).

  40. Ex. 60.40Answer key

    What is geometrically the linearization L(x)L(x) of ff at aa?

  41. Ex. 60.41

    The radius of a sphere is r=5r = 5 cm with a measurement error of dr=0.1dr = 0.1 cm. Use differentials to estimate the absolute and relative error in the volume V=43πr3V = \tfrac{4}{3}\pi r^3.

  42. Ex. 60.42

    If the relative error in the radius of a sphere is 1%1\%, what is the relative error in the volume? Justify with differentials.

  43. Ex. 60.43Answer key

    The volume of a sphere is increasing at 22 cm³/s. What is dr/dtdr/dt when r=2r = 2 cm?

  44. Ex. 60.44

    An inverted cone has radius/height ratio r/h=1/2r/h = 1/2. Water flows in at 33 m³/min. What is dh/dtdh/dt when h=2h = 2 m?

  45. Ex. 60.45

    An 8 m ladder leans against a wall. The foot of the ladder slides away from the wall at 11 m/s. How fast is the top of the ladder sliding down the wall when the foot is 55 m from the wall?

  46. Ex. 60.46Answer key

    Two cars start from a crossing: one travels north at 4040 km/h, the other east at 3030 km/h. What is the rate of change of the distance between them when the first car has traveled 44 km and the second 33 km?

  47. Ex. 60.47

    Show that if the radius of a circle grows at a constant rate cc cm/s, then the rate of change of the area is proportional to the radius rr.

  48. Ex. 60.48

    The radius of a circle is growing at 11 cm/s. Compute the rate of change of the area when r=3r = 3 cm.

  49. Ex. 60.49

    Analyze the differentiability of f(x)=xf(x) = |x| at x=0x = 0.

  50. Ex. 60.50

    Determine aa and bb such that f(x)={x2,x<1ax+b,x1f(x) = \begin{cases} x^2, & x < 1 \\ ax + b, & x \geq 1 \end{cases} is of class C1C^1 at x=1x = 1.

Sources

  • Active Calculus — Boelkins · 2024 · ch. 1–3. Primary source. CC-BY-NC-SA.
  • Calculus, Volume 1 — OpenStax · 2016 · §3.1–3.9, §4.1–4.2. CC-BY-NC-SA.
  • APEX Calculus — Hartman et al. · 2024 · v5 · ch. 2. CC-BY-NC.

Updated on 2024-07-27 · Author(s): Clube da Matemática

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