How to Use the Half-Angle Formula for (cosx)^2?

  • Thread starter Thread starter nameVoid
  • Start date Start date
  • Tags Tags
    Angle Formula
Click For Summary
SUMMARY

The discussion focuses on using the half-angle formula to solve the integral of y=sin2x, bounded by x=0 and x=π, when revolved around the x-axis. The cross-section area is defined as A=π(sin2x)². Participants suggest utilizing the identity cos(2x) = 1 - 2sin²(x) to derive the half-angle formula. The Pythagorean identity is also recommended to transform sin²(x) into (1-cos(2x))/2, facilitating easier integration.

PREREQUISITES
  • Understanding of integral calculus and area of revolution
  • Familiarity with trigonometric identities, specifically half-angle formulas
  • Knowledge of substitution methods in integration
  • Proficiency in manipulating Pythagorean identities
NEXT STEPS
  • Study the derivation and application of half-angle formulas in trigonometry
  • Learn about the Pythagorean identity and its uses in calculus
  • Practice integration techniques involving trigonometric functions
  • Explore the method of cylindrical shells for volume of revolution problems
USEFUL FOR

Students and educators in calculus, mathematicians focusing on integration techniques, and anyone seeking to deepen their understanding of trigonometric identities and their applications in solving integrals.

nameVoid
Messages
238
Reaction score
0
y=sin2x bounded by x=0,x=pi,y=0 , revolved around the x-axis

cross section A=pi(sin2x)^2

latex2png.2.php?z=100&eq=pi%5Cint_%7B0%7D%5E%7Bpi%2F2%7D%20(sin(2x))%5E2.jpg


latex2png.2.php?z=100&eq=4pi%5Cint_%7B0%7D%5E%7Bpi%2F2%7Dsin%5E2xcos%5E2x.jpg

taking u = sinx ; du=cosxdx

im unclear on how to proceed in this case where du needs to satisfy (cosx)^2
the problem hints to use a half angle formula
 
Physics news on Phys.org


Try the identity cos(2x) = 1 - 2sin2(x). It can be rearranged to be a half-angle formula. :smile:
 


still i am unclear on how to proceed here
 


nameVoid said:
still i am unclear on how to proceed here

Try using the Pythagorean identity to get sin2(x) - sin4(x), then apply the half angle formula to get cosines (twice for the second term) that are not squared.
 


slider142 is trying to say that since sin^2(x)=(1-cos(2x))/2, sin^(2x)=(1-cos(4x))/2. That's pretty easy to integrate.
 


perfect
 

Similar threads

Replies
3
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
4
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
Replies
5
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 12 ·
Replies
12
Views
33K
  • · Replies 3 ·
Replies
3
Views
2K