I need help understanding trigonometric identities  TOPIC_SOLVED

Trigonometric ratios and functions, the unit circle, inverse trig functions, identities, trig graphs, etc.

I need help understanding trigonometric identities

Postby Wags on Fri Oct 22, 2010 1:01 am

Hello, I'm a sophomore in high school that started Algebra 2 & Trigonometry this year, so I am a first year student of trig with little experience with it. I do not understand the trigonometric identities. I have a list of trigonometric identities in my notes, but I don't know how to use them in order to solve a problem.

Example from my homework:

Solve for values of between 0o and 90o.
If Cos =, find Sin.

Where exactly would I start with this equation? I was thinking I would use the Pythagorean identity "Sin2+Cos2=1"; however, I am not sure.

How would I solve this problem if the value of is between 180o and 270o. What about between 270o and 360o?
Wags
 
Posts: 1
Joined: Fri Oct 22, 2010 12:38 am

Sponsor

Sponsor
 

Re: I need help understanding trigonometric identities  TOPIC_SOLVED

Postby Martingale on Fri Oct 22, 2010 2:07 am

Wags wrote:Hello, I'm a sophomore in high school that started Algebra 2 & Trigonometry this year, so I am a first year student of trig with little experience with it. I do not understand the trigonometric identities. I have a list of trigonometric identities in my notes, but I don't know how to use them in order to solve a problem.

Example from my homework:

Solve for values of between 0o and 90o.
If Cos =, find Sin.

Where exactly would I start with this equation? I was thinking I would use the Pythagorean identity "Sin2+Cos2=1"; however, I am not sure.


you can use that.
User avatar
Martingale
 
Posts: 363
Joined: Mon Mar 30, 2009 1:30 pm
Location: USA

Re: I need help understanding trigonometric identities

Postby trgreene42 on Tue Nov 30, 2010 11:06 am

sin^2+cos^2=1
thus
If cos theta= (5/13)

sin^2+(5/13)^2=1

sin^2+(25/169)=1

sin^2=(169/169)-(25/169)

sin^2=(144/169)

sin theta= sqrt of (144/169)

sin theta= (12/13)
trgreene42
 
Posts: 1
Joined: Tue Nov 30, 2010 10:51 am

Re: I need help understanding trigonometric identities

Postby Martingale on Tue Nov 30, 2010 1:48 pm

another way is to notice that is adj/hyp on a right triangle



this creates a 5,12,13 triangle: adj=5, opp=12, hyp=13


which is opp over hyp is therefore
User avatar
Martingale
 
Posts: 363
Joined: Mon Mar 30, 2009 1:30 pm
Location: USA


Return to Trigonometry

cron