Question:

\(∫\frac{dx}{\sqrt{9x-4x^2}}\) equals

Updated On: Sep 15, 2023
  • \(\frac{1}{9}sin^{-1}(\frac{9x-8}{8})+C\)

  • \(\frac{1}{2}sin^{-1}(\frac{8x-9}{9})+C\)

  • \(\frac{1}{3}sin^{-1}(\frac{9x-8}{8})+C\)

  • \(\frac{1}{2}sin^{-1}(\frac{9x-8}{9})+C\)

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The Correct Option is B

Solution and Explanation

The correct answer is B: \(= \frac{1}{2}sin^{-1}(\frac{8x-9}{9})+C\)
\(∫\frac{dx}{\sqrt{9x-4x^2}}\)
\(= ∫\frac{1}{\sqrt{-4(x^2-\frac{9}{4x})}}dx\)
\(= ∫\frac{1}{-4(x^2-\frac{9}{4}x+\frac{81}{64}-\frac{81}{64})}dx\)
\(= ∫\frac{1}{\sqrt{-4[(x-\frac{9}{8})^2-(\frac{9}{8})^2}}] dx\)
\(=\frac{1}{2} ∫\frac{1}{\sqrt{(\frac{9}{8})^2 - (x-\frac{9}{8})^2}} dx\)
\(=\frac{1}{2}[sin^{-1}\bigg(\frac{x-\frac{9}{8}}{\frac{9}{8}}\bigg)]+C\)                              \(( ∫\frac{dy}{\sqrt{a^2-y^2}} = sin^{-1} \frac{y}{a}+C)\)
\(= \frac{1}{2}sin^{-1}(\frac{8x-9}{9})+C\)
Hence, the correct Answer is B.
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Concepts Used:

Integrals of Some Particular Functions

There are many important integration formulas which are applied to integrate many other standard integrals. In this article, we will take a look at the integrals of these particular functions and see how they are used in several other standard integrals.

Integrals of Some Particular Functions:

  • ∫1/(x2 – a2) dx = (1/2a) log|(x – a)/(x + a)| + C
  • ∫1/(a2 – x2) dx = (1/2a) log|(a + x)/(a – x)| + C
  • ∫1/(x2 + a2) dx = (1/a) tan-1(x/a) + C
  • ∫1/√(x2 – a2) dx = log|x + √(x2 – a2)| + C
  • ∫1/√(a2 – x2) dx = sin-1(x/a) + C
  • ∫1/√(x2 + a2) dx = log|x + √(x2 + a2)| + C

These are tabulated below along with the meaning of each part.