Solving Trigonometric Equations like 2 cosx - 1 = 0

[Anthony 21x]

If I have something like 2 cosx -1 = 0 I understand you first simplify making cosx=1/2; once you get there, how do you solve for x?

 

[mmm4444bot]

What angle has a cosine of 1/2?

Use this as a reference angle to write a formula for all angles whose cosine is 1/2, or restrict the domain for x.

 

[Anthony 21x]

Re: Solving Trigonometric Equations

The question you asked is actually the problem I've been having. I don't get how to find what angle would have a cos of 1/2 in other words. I've read the part in my book 1000 times but the book we have is horrible, and of course this is an online class so there is no lecture to explain it.

How would I go about finding an angle that has a cos of 1/2?

 

[Anthony 21x]

Re: Solving Trigonometric Equations

is this where you multiply your answer by square root of 2 divided by 2??

 

[Anthony 21x]

Re: Solving Trigonometric Equations

I know you can do it just by looking at the unit circle if you have a standard angle, but what if you have something where the angle is 22.56* (.1253 X Pie radian)

 

[Deleted member 4993]

Re: Solving Trigonometric Equations

I know you can do it just by looking at the unit circle if you have a standard angle, but what if you have something where the angle is 22.56* (.1253 X Pie radian)

Then use calculator - or archaic tables (if you can find one).

 

[Anthony 21x]

so how would you find the answer to something like cos x = 1/5.1284 ?
(a question from the test I just took)

I tried using guess and check, no luck.

 

[stapel]

so how would you find the answer to something like cos x = 1/5.1284 ?

You'd use what you learned about inverse-trig functions, and plug the value into your calculator.

Eliz.