Trigonometric Identity Verification | Simplifying sin(4x) and Solving for x

  • Thread starter Thread starter themadhatter1
  • Start date Start date
  • Tags Tags
    Identity
Click For Summary
SUMMARY

The discussion focuses on the verification of the trigonometric identity sin(4x) = 8cos^3(x)sin(x) - 4sin(x)cos(x). The solution process involves applying various trigonometric identities, including the double angle identity and the Pythagorean identity, to simplify the equation. The final verification confirms that both sides of the equation are equal, demonstrating the identity holds true. The participant successfully navigates through the simplification steps to arrive at the conclusion.

PREREQUISITES
  • Understanding of trigonometric identities, including double angle and half angle identities.
  • Familiarity with the Pythagorean identity in trigonometry.
  • Ability to perform algebraic simplifications using FOIL (First, Outside, Inside, Last) method.
  • Knowledge of how to manipulate sine and cosine functions in equations.
NEXT STEPS
  • Study the derivation and applications of the double angle identity for sine and cosine.
  • Explore the Pythagorean identity and its implications in solving trigonometric equations.
  • Learn advanced techniques for simplifying trigonometric expressions, including the use of FOIL.
  • Investigate the relationship between sine and cosine functions in various trigonometric identities.
USEFUL FOR

Students studying trigonometry, mathematics educators, and anyone looking to deepen their understanding of trigonometric identities and simplification techniques.

themadhatter1
Messages
139
Reaction score
0

Homework Statement



sin(4x) = 8cos3(x)sin(x)-4sin(x)cos(x)

Homework Equations



All trigonometric identities

The Attempt at a Solution



I can simplify the right side using the double angle identity to:

sin(4x) = 4sin(2x)cos2(x)-2sin(2x)

However, now I'm not sure what to do. Did I take a step in the wrong direction?
 
Physics news on Phys.org
Never mind, I found the solution myself, here is my process. I was on the right track.

sin(4x) = 4sin(2x)cos2(x)-2sin(2x)

Pythagorean Identity:

sin(4x) = 4sin(2x)(1-sin2x)-2sin(2x)

FOIL:

sin(4x) = 4sin(2x)-4sin(2x)sin2(x)-2sin(2x)

Half Angle Identity:

sin(4x) = 4sin(2x)-4sin(2x)[(1-cos(2x)/2]-2sin(2x)

simplify:

sin(4x) = 4sin(2x)-[4sin(2x)+4sin(2x)cos(2x)]/(2)-2sin(2x)

simplify more:

sin(4x) = 4sin(2x)-2sin(2x)+2sin(2x)cos(2x)-2sin(2x)

sin(4x) = 4sin(2x)-4sin(2x)+2sin(2x)cos(2x)

sin(4x) = 2sin(2x)cos(2x)

Double Angle Identity:

sin(4x) = sin(4x)
 
You can save yourself a lot of typing by working from the left side to the right.

sin(4x) = sin(2(2x)) = 2sin(2x)cos(2x)
= 4sin(x)cos(x)(cos2(x) - sin2(x))
= 4sin(x)cos(x)(2cos2(x) - 1)
= 8sin(x)cos3(x) - 4sin(x)cos(x)
QED
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
Replies
10
Views
2K
Replies
1
Views
3K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
5
Views
2K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K