Partial Fraction Decomposition problem

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SUMMARY

The forum discussion centers on solving the integral ∫((secx)^2)/[((tanx)^2)+(3tanx)+2] using partial fraction decomposition. The correct solution involves a u-substitution, completing the square, and a trigonometric substitution, leading to the answer -2lnabs(1/(2tanx+3)+√(4(tanx+3/2)²-1)). Participants identified errors in the initial approach, particularly in the interpretation of trigonometric identities. The discussion emphasizes the importance of careful algebraic manipulation and verification of methods in calculus.

PREREQUISITES
  • Understanding of integral calculus
  • Familiarity with partial fraction decomposition
  • Knowledge of trigonometric identities, specifically secant and tangent functions
  • Experience with u-substitution and completing the square techniques
NEXT STEPS
  • Study advanced techniques in integral calculus, focusing on trigonometric substitutions
  • Practice additional problems involving partial fraction decomposition
  • Review the properties and applications of secant and tangent functions
  • Explore common pitfalls in algebraic manipulation during calculus problems
USEFUL FOR

Students studying calculus, particularly those tackling integrals involving trigonometric functions, and educators looking for examples of common errors in partial fraction decomposition.

sashab
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Homework Statement



Evaluate ∫((secx)^2)/[((tanx)^2)+(3tanx)+2]

Homework Equations



Partial fraction decomposition

The Attempt at a Solution



So here's what I did:
tumblr_n3y124QYZc1tsd2vco1_500.jpg


But this is incorrect. It says the correct answer is -2lnabs(\frac{1}{2tanx+3}+\sqrt{4(tanx+3/2)^{2}-1}), which was achieved by making the same u-substitution, completing the square, and then doing a trig substitution. I'm not sure why my method is incorrect. Any help would be great, thanks!
 
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I agree with your answer (and method!). Seems to me that the other answer is a decreasing function in the range 0 to 1, yet from the integral it should clearly be increasing. If you post all the working of the other method I'll see if I can find the error.
 
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Ohh okay, I'm glad it's not incorrect then! Here's the other solution I was referring to :
tumblr_n3y5ulxl4Q1tsd2vco1_1280.png
 
There's an error here: csc = 1/sec.
 
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haruspex said:
There's an error here: csc = 1/sec.
Ohh okay I see. Thanks so much for the help! Would you be willing to help me with another partial fraction decomposition question?
 
sashab said:
Ohh okay I see. Thanks so much for the help! Would you be willing to help me with another partial fraction decomposition question?
Sure, but post it in a new thread for all to see.
 

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