• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Trigonometric inequality

  • Thread starter IsrTor
  • Start date
1. The problem statement, all variables and given/known data
solve the inequality:
-1[tex]\leq[/tex] 1[tex]/[/tex](1+cosx) [tex]\leq[/tex]1

3. The attempt at a solution

firstly cosx does not equal -1 but you'll see doesn't help much
-1<cosx<1
0<cosx+1<2
that makes the above equation 1/(1+cosx) between 0.5 and infinity. but I have no clue as to how to find the set of x which solve the inequality
 

tiny-tim

Science Advisor
Homework Helper
25,790
242
solve the inequality:
-1[tex]\leq[/tex] 1[tex]/[/tex](1+cosx) [tex]\leq[/tex]1
Hi IsrTor! :smile:

You need to learn your trigonometric identities …

what does 1 + cosx also equal? :wink:
 
32,389
4,151
1. The problem statement, all variables and given/known data
solve the inequality:
-1[tex]\leq[/tex] 1[tex]/[/tex](1+cosx) [tex]\leq[/tex]1

3. The attempt at a solution

firstly cosx does not equal -1 but you'll see doesn't help much
-1<cosx<1
0<cosx+1<2
that makes the above equation 1/(1+cosx) between 0.5 and infinity. but I have no clue as to how to find the set of x which solve the inequality
Since 1/(1 + cosx) is between -1 and 1, its reciprocal has to be larger than 1 or smaller than -1, depending on whether 1/(1 + cos x) is positive or negative, respectively.

Can you do something with that?
 

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top