Can Trig Identities Be Proven Using Basic Trigonometric Functions?

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SUMMARY

The discussion confirms that trigonometric identities can indeed be proven using basic trigonometric functions. Specifically, the identity \((\tan^2 x -1)/\sec^2 x = -\cos(2x)\) is established through a series of transformations involving \(\tan^2 x\), \(\sec^2 x\), and the Pythagorean identity. The proof demonstrates the efficiency of using fundamental trigonometric relationships to derive complex identities.

PREREQUISITES
  • Understanding of basic trigonometric functions: sine, cosine, tangent
  • Familiarity with trigonometric identities and their applications
  • Knowledge of the Pythagorean identity: \(\sin^2 x + \cos^2 x = 1\)
  • Ability to manipulate algebraic expressions involving trigonometric functions
NEXT STEPS
  • Study the derivation of the double angle formulas for sine and cosine
  • Explore advanced trigonometric identities and their proofs
  • Learn about the unit circle and its relationship to trigonometric functions
  • Practice solving trigonometric equations using identities
USEFUL FOR

Students of mathematics, educators teaching trigonometry, and anyone interested in deepening their understanding of trigonometric identities and their proofs.

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Homework Statement
I believed I've proved it right, but can someone confirm?
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I believe it is correct, but note that

$$(\tan^2 x -1)/\sec^2 x = (\tan^2 x -1) \cos^2 x = \sin^2 x - \cos^2 x = - \cos(2x)$$

so you could have been a little faster.
 
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