Trigonometric Equations

  • Thread starter TbbZz
  • Start date
  • #1
37
0

Homework Statement


sinx + cosx = 0


Homework Equations


N/A


The Attempt at a Solution



sinx + cosx = 0

sinx = -cosx
sinx = (+/-) sqrt(sin^2x - 1)
(sinx)^2 = (+/-) sqrt(sin^2x - 1)^2
sinx = sin^2x - 1

Not really too sure what to do from here on.

The answer is 3[tex]\pi[/tex]/4 and 7[tex]\pi[/tex]/4.

I appreciate the help, thanks in advance.
 

Answers and Replies

  • #2
1,753
1
[tex]sin x = -\cos x[/tex]

Divide by cosx, what identity do you get?
 
  • #3
HallsofIvy
Science Advisor
Homework Helper
41,847
966
Or, since you have gone to all the work of getting to [itex]sin(x)= sin^2(x)- 1[/tex], let y= sin(x) and rewrite it as y^2- y- 1= 0. solve that quadratic equation for y and then solve sin(x)= y.
 
Last edited by a moderator:
  • #4
37
0
Divide by cosx, what identity do you get?

Thank you for the assistance, I can't believe I missed that!
 

Related Threads on Trigonometric Equations

  • Last Post
Replies
2
Views
941
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
7
Views
1K
  • Last Post
Replies
9
Views
2K
  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
5
Views
981
  • Last Post
Replies
5
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
4
Views
2K
Top