Trigonometry sin cos tan Question

  • Thread starter 404
  • Start date

404

52
0
If Sin(theta) = 1/3 and cos(theta) < 0, find the value(s) for tan(theta)
How do I do this? Thanks.
 

mathwonk

Science Advisor
Homework Helper
10,730
908
recall the emanings, with a picture, of these functions sin, cos, tan, using a unit circle. you may be able to just see it.
 

HallsofIvy

Science Advisor
Homework Helper
41,709
876
Do you know that sin2(&theta;)+ cos2(&theta;)= 1? Since you know sin(&theta;)= 1/3, you can use that to find cos(&theta;). Now, how is tan(&theta;) defined?
 
195
0
404 said:
How do I do this? Thanks.
Take the arc sin of 1/3 - this will give you the angle, but it will be the principle angle (first quadrant). But, since Cos theta <0, you know it can't be in the first quadrant or fourth quadrant, so it must be in either the second or third quadrant. But, since sin theta is >0, it must be in the second quadrant. You should be able to get the correct angle from this info, and therefore the correct cosine and then - as was hinted before - remember the definition of tangent theta.
 

404

52
0
I got it now, Thanks guys :)
 

Related Threads for: Trigonometry sin cos tan Question

  • Posted
Replies
4
Views
616
  • Posted
Replies
3
Views
2K
  • Posted
Replies
4
Views
2K
  • Posted
Replies
2
Views
2K
  • Posted
Replies
2
Views
2K
  • Posted
Replies
16
Views
9K
  • Posted
2
Replies
31
Views
4K
  • Posted
Replies
5
Views
16K

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

Hot Threads

Top