So what can you do for this integral?

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SUMMARY

The integral \(\int \frac{1}{\sec x + \tan x} \, dx\) cannot be evaluated simply as \(\ln|\sec x + \tan x| + C\). This misconception arises from the incorrect assumption that the integral of \(\frac{1}{f(x)}\) is always \(\ln|f(x)| + C\), which only holds true when \(f(x) = x\). To correctly evaluate this integral, one must express \(\tan x\) in terms of sine and cosine and recognize that \(\sec x\) is the reciprocal of cosine.

PREREQUISITES
  • Understanding of basic integral calculus
  • Familiarity with trigonometric identities, specifically \(\sec x\) and \(\tan x\)
  • Knowledge of logarithmic differentiation
  • Ability to manipulate algebraic expressions involving trigonometric functions
NEXT STEPS
  • Learn techniques for integrating trigonometric functions, particularly \(\int \frac{1}{\sec x + \tan x} \, dx\)
  • Study the derivation and application of trigonometric identities
  • Explore the concept of logarithmic differentiation in calculus
  • Investigate common misconceptions in integral calculus to avoid errors
USEFUL FOR

Students studying calculus, particularly those focusing on integral calculus, as well as educators looking to clarify common misunderstandings in evaluating integrals involving trigonometric functions.

whatlifeforme
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Homework Statement


evaluate the integral.


Homework Equations



\displaystyle\int {\frac{1}{secx+tanx} dx}

The Attempt at a Solution


can i just do ln|secx + tanx| ??
 
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whatlifeforme said:

Homework Statement


evaluate the integral.

Homework Equations



\displaystyle\int {\frac{1}{secx+tanx} dx}

The Attempt at a Solution


can i just do ln|secx + tanx| ??
Probably not.

What's the derivative of ln|secx + tanx| ?

Added in Edit:

Write the tangent in terms of sine & cosine and the secant as the reciprocal of the cosine.
 
Last edited:
whatlifeforme said:

Homework Statement


evaluate the integral.

Homework Equations



\displaystyle\int {\frac{1}{secx+tanx} dx}

The Attempt at a Solution


can i just do ln|secx + tanx| ??

No. You're making the same mistake you made in this thread: https://www.physicsforums.com/showthread.php?t=678488.

It is NOT TRUE[/color] that
$$ \int \frac{dx}{f(x)} = ln|f(x)| + C$$

The above is true only if f(x) = x, which is certainly not the case here.
 

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