Prove Trig Identities: sec(2x) - tan(2x) & cos(2x)/(1 + sin(2x))

  • Thread starter Thread starter Hockeystar
  • Start date Start date
  • Tags Tags
    Trig
Click For Summary
SUMMARY

The discussion focuses on proving two trigonometric identities: sec(2x) - tan(2x) = (cos(x) - sin(x))/(cos(x) + sin(x)) and cos(2x)/(1 + sin(2x)) = tan(π/4 - x). Participants engage in simplifying expressions, particularly using the identity for cos(2x) to facilitate the proof. The conversation highlights the importance of recognizing equivalent forms of trigonometric functions to achieve the desired results.

PREREQUISITES
  • Understanding of basic trigonometric identities
  • Familiarity with the double angle formulas for sine and cosine
  • Ability to manipulate algebraic expressions involving trigonometric functions
  • Knowledge of the tangent function and its properties
NEXT STEPS
  • Study the derivation of double angle formulas for sine and cosine
  • Practice proving trigonometric identities using algebraic manipulation
  • Explore the relationship between tangent and other trigonometric functions
  • Learn about the unit circle and its application in trigonometric proofs
USEFUL FOR

Students studying trigonometry, educators teaching trigonometric identities, and anyone looking to enhance their skills in proving mathematical identities.

Hockeystar
Messages
61
Reaction score
0

Homework Statement


Teacher gave this identity twice to us but the starting position slightly varies.

Prove sec(2x) - tan(2x) = (cos(x)-sin(x))/(cos(x) + sin(x))

Prove cos(2x)/(1 + sin(2x)) = tan(pi/4-x)


Homework Equations


pretty much all trig identities


The Attempt at a Solution



I get to (1-sin(2x))/cos(2x) = (cos(x)-sin(x))/(cos(x) + sin(x)) and then I'm stumped.
 
Physics news on Phys.org
Welcome to PF!

Hi Hockeystar! Welcome to PF! :wink:
Hockeystar said:
I get to (1-sin(2x))/cos(2x) = (cos(x)-sin(x))/(cos(x) + sin(x))

ok so far :rolleyes:

now what is cos(2x) ? :smile:
 
cosx - sinx(cosx + sinx). How does that help me cancel out something?
 
Hockeystar said:
cosx - sinx(cosx + sinx). How does that help me cancel out something?

You mean (cosx - sinx)(cosx + sinx) …

It doesn't have to cancel to help :wink:

think! look at the RHS!
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
3K
Replies
5
Views
2K
  • · Replies 18 ·
Replies
18
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
Replies
54
Views
4K
Replies
5
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K