Solve cos2xsinx=1: Simplifying and Finding X

  • Thread starter Thread starter CutiePieYum
  • Start date Start date
Click For Summary
To solve the equation cos(2x)sin(x) = 1, it is essential to recognize that both cos(2x) and sin(x) can only reach a maximum value of 1. This leads to the conditions where cos(2x) must equal 1 and sin(x) must equal 1, or both must equal -1, but these conditions cannot be satisfied simultaneously. The discussion suggests graphing cos(2x) and sin(x) over the interval [0, 2π] to visualize potential intersections. Additionally, transforming the equation into a cubic form by substituting sin(x) with u can help identify real roots. Ultimately, finding the solutions requires careful analysis of these transformations and graphical representations.
CutiePieYum
Messages
3
Reaction score
0

Homework Statement


Simplify AND Solve for X
cos2xsinx=1


Homework Equations


The triples, doubles


The Attempt at a Solution


cos2xsinx=1
(cos^2x-sin^2x)(sinx)=1
(-1x)(sinx)=1
-sinx=1
sinx= -1
?


..

:-/

Help.. :)
 
Physics news on Phys.org


The maximum absolute value of cos(2x) and sin(x) is 1. So the only way you can solve that is if cos(2x)=1 AND sin(x)=1 or cos(2x)=(-1) AND sin(x)=(-1). Is either of those possible? If so which one?
 


I have no idea may i have another clue
 


anyone?
 


CutiePieYum said:
I have no idea may i have another clue

Graph cos(2x) and sin(x) on [0,2pi]. Or do this cos^2(x)-sin^2(x)=1-2*sin^2(x). So you have (1-2*sin^2(x))*sin(x)=1. If sin(x)=u then you have (1-2*u^2)*u=1. That's a cubic equation for u. Can you find the real root?
 
Last edited:

Similar threads

  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 11 ·
Replies
11
Views
2K
Replies
5
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
5
Views
2K
  • · Replies 4 ·
Replies
4
Views
7K