Finding the Final Sum of Trigonometric Functions: Cosine and Sine Formulas

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SUMMARY

The discussion focuses on finding the finite sum of trigonometric functions, specifically the sums of cos²x and sin²x for n terms. Participants explore the use of complex numbers, specifically the expression z = A + Bi, where A and B represent the sums of cosine and sine functions, respectively. They discuss the geometric series and the application of Euler's formula to derive the sums. The final results are expressed in terms of trigonometric identities and complex numbers, leading to the conclusion that the sums can be represented as A = (n + (cos(n+1)x sin(nx))/sin(x))/2 and B = (n - (cos(n+1)x sin(nx))/sin(x))/2.

PREREQUISITES
  • Understanding of trigonometric identities, particularly Pythagorean identities.
  • Familiarity with complex numbers and their representation in the form A + Bi.
  • Knowledge of geometric series and their summation techniques.
  • Proficiency in using Euler's formula for complex exponentials.
NEXT STEPS
  • Study the derivation of the sum of finite geometric series.
  • Learn how to apply Euler's formula in trigonometric contexts.
  • Explore the relationship between complex numbers and trigonometric functions.
  • Investigate the use of double angle formulas in simplifying trigonometric expressions.
USEFUL FOR

Mathematics students, educators, and anyone interested in advanced trigonometric identities and their applications in complex analysis.

  • #61
Physicsissuef said:
Am I right?


Yes!
 
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  • #62
D H said:
Does helping the exact same person on the exact same question with the exact same frustration level but in another forum count?

It counts double.
 
  • #63
But can you tell me please how did they simplify it?
 
  • #64
I think you should try it first. I don't see any '2' factors in the final result. So you might start with a double angle formula.
 
  • #65
\frac{cos^2x-sin^2x+cos^2nx-sin^2nx-cos^2(n+1)x+sin^2(n+1)x-sin^2x-cos^2x}{4sin^2x}

\frac{-2sin^2x+cos^2nx-sin^2nx-cos^2(n+1)x+sin^2(n+1)x}{4sin^2x}

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