hw help: trig equations

pr3ttylilprobl3m · May 21st 2009, 4:13pm

Ok, so I'm homeschooled. I teach myself. This has never been a problem, until I got to trig equations. I don't get them at all! And the lesson provides me with maybe 4 problems to practice with before I have to start doing work on my own. So if anyone could help me with a few of these problems? You will be my hero for FOREVER!! haha.

The one I'm having the big problem with right now is:

cot 2x = - sqr root (3)

I'm sure it's a simple answer, but I just don't even know where to start.

If anyone knows of a REALLY good site where I could find practice problems with the answers and work done, that would be great, too!!

ensy · May 21st 2009, 4:21pm

there is a formula for that. use the formula.

---------- Post added at 11:21 PM ---------- Previous post was at 11:21 PM ----------

i forgot what it is though

pr3ttylilprobl3m · May 21st 2009, 4:21pm

ensy wrote:

there is a formula for that. use the formula.

---------- Post added at 11:21 PM ---------- Previous post was at 11:21 PM ----------

i forgot what it is though

what formula?

tg4 · May 21st 2009, 4:46pm

So is the equation cos2x=-root 3?

pr3ttylilprobl3m · May 21st 2009, 4:46pm

yep. and im spose to be solving for x

Bosh Bash Bish · May 21st 2009, 4:49pm

Isnt trig ermm SOHCAHTOA?

tg4 · May 21st 2009, 4:51pm

Yeah, trig's SOHCAHTOA. I'm just trying to work out that equation... I'm used to using trig with triangles. Is there a graph or anything else with the equation?

pr3ttylilprobl3m · May 21st 2009, 5:02pm

noooope. it's basically like trig identities, but instead of proving that one side equals the other, your solving for the unknown angle. You can use identities to simplify and stuff, but then you just have to solve for x.

Bosh Bash Bish · May 21st 2009, 5:02pm

Yeahh I've only ever used trig with triangles.

tg4 · May 21st 2009, 5:07pm

Well, if it's any help I have 2 formulas for the cosine rule.

a squared = b squared + c squared - 2bcCOSA

or

COSA = (b squared + c squared - a squared) divided by 2bc

I hope that's some help.

Techno Viking · May 21st 2009, 9:20pm

I think you have to use this
cos2A = cos^2A − sin^2A
So it becomes cos^2x - sin^2x = root3
I think now that you know this you can use the exact value triangles to show that these equal root3/1 which would be just root3

I've not done what your doing in school thouhg so i'm probably miles off

LOLFag · May 22nd 2009, 5:28pm

Is this at precalculus level or calculus? Because I don't know if I should provide the easier solutio. Or the harder one.

By the way, all of you are on the wrong track. The answer is much simpler than you think. It's cotangent here, not cosine! Simply draw a 30-60-90 triangle in the third quadrant, root 3 on the x axis!

The rest is self explanatory. Simply put, the answer is 165, as confirmed on the calculator. Very very basic stuff here.

hw help: trig equations

hw help: trig equations

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