Math 2.0

Real functions Concept

Trigonometric substitution

Builds on Integration by substitutionPythagorean trigonometric identity

Summary

Trigonometric substitution is a substitution method for integrals that contain a2−x2\sqrt{a^2 - x^2}, a2+x2\sqrt{a^2 + x^2}, or x2−a2\sqrt{x^2 - a^2}. We set xx equal to asin⁡θa \sin \theta, atan⁡θa \tan \theta, or asec⁡θa \sec \theta. The Pythagorean identity then removes the square root.

Remarks

With x=asin⁡θx = a \sin \theta for θ∈[−π/2,π/2]\theta \in [-\pi/2, \pi/2], we get a2−x2=acos⁡θ\sqrt{a^2 - x^2} = a \cos \theta, for a>0a > 0. For example, this substitution gives ∫−111−x2 dx=π/2\int_{-1}^{1} \sqrt{1 - x^2} \, dx = \pi/2, the area of a half disc. Hyperbolic functions can replace the trigonometric functions in the second and the third case.

Reading path

To understand this page from the ground up, read these 88 pages in order. The foundations come first.

  1. Limit point of a set definition
  2. Local maximum definition
  3. Partition of an interval definition
  4. Sequence definition
  5. Limit of a function definition
  6. Local minimum definition
  7. Mesh of a partition definition
  8. Riemann sum definition
  9. Real sequence definition
  10. Subsequence definition
  11. Continuity at a point definition
  12. Derivative definition
  13. Riemann integrable function definition
  14. Bounded sequence definition
  15. Cauchy sequence definition
  16. Geometric sequence definition
  17. Limit of a sequence definition
  18. Monotone sequence definition
  19. Series definition
  20. Continuous function definition
  21. Epsilon-delta definition of continuity statement
  22. Antiderivative definition
  23. Differentiable function definition
  24. Fermat's theorem on stationary points statement
  25. Riemann integral definition
  26. Upper and lower Darboux sums definition
  27. Limit superior definition
  28. Cauchy sequences are bounded statement
  29. Sum of a finite geometric series statement
  30. Monotone convergence theorem for sequences statement
  31. Convergent sequence definition
  32. Every sequence has a monotone subsequence statement
  33. Pointwise convergence definition
  34. Squeeze theorem statement
  35. Partial sum definition
  36. Power series definition
  37. Intermediate value theorem statement
  38. Composition of continuous functions is continuous statement
  39. Uniform continuity definition
  40. Derivative function definition
  41. Definite integral definition
  42. Upper and lower Darboux integrals definition
  43. Bolzano–Weierstrass theorem statement
  44. The sequence r^n tends to zero for |r| < 1 example
  45. Radius of convergence definition
  46. Convergent series definition
  47. Uniform convergence definition
  48. Sine and cosine definition
  49. Chain rule statement
  50. Uniform continuity on a set definition
  51. Boundedness theorem statement
  52. Higher derivative definition
  53. Monotonicity of the integral statement
  54. Additivity of the integral over intervals statement
  55. Darboux and Riemann integrals agree statement
  56. Cauchy criterion for sequences statement
  57. Absolute convergence definition
  58. Uniform convergence on a set definition
  59. Series of functions definition
  60. A series of nonnegative terms converges iff its partial sums are bounded statement
  61. Sum of a series definition
  62. Extreme value theorem statement
  63. Continuously differentiable function definition
  64. Continuous functions on a closed bounded interval are uniformly continuous statement
  65. Riemann's criterion for integrability statement
  66. Uniformly Cauchy sequence of functions definition
  67. Geometric series example
  68. Comparison test statement
  69. Mean value theorem for integrals statement
  70. Rolle's theorem statement
  71. Continuous functions are Riemann integrable statement
  72. Root test statement
  73. Weierstrass M-test statement
  74. Mean value theorem statement
  75. First fundamental theorem of calculus statement
  76. Cauchy–Hadamard theorem statement
  77. Power series converge uniformly on smaller discs inside the radius of convergence statement
  78. A function with zero derivative is constant statement
  79. Second fundamental theorem of calculus statement
  80. The integral of a continuous function is an antiderivative statement
  81. Uniform convergence of derivatives allows term-by-term differentiation statement
  82. Integration by substitution statement
  83. Term-by-term differentiation statement
  84. Power series are differentiable inside the radius of convergence statement
  85. Derivative of cosine statement
  86. Derivative of sine statement
  87. Pythagorean trigonometric identity statement
  88. Trigonometric substitution concept

Further reading

  1. Web https://en.wikipedia.org/wiki/Trigonometric_substitution, lead section
About this page
Tag0EAR3KNRTN
URIm2://0EAR3KNRTN
Kindconcept
WritingW0 stub
MSC26A36
UsesIntegration by substitution, Pythagorean trigonometric identity
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