if cos 2 theta = -0.5625 how do i find theta?

[mr paul]

if cos 2 theta = -0.5625 how do i find theta?

 

[Deleted member 4993]

if cos 2 theta = -0.5625 how do i find theta?

Do you have a scientific calculator that has a cos^-1 button?

Also you could use wolframalpha.com ...

 

[pythagorean314159]

what are you saying?

if cos 2 theta = -0.5625 how do i find theta?

Are you saying "If cos (2*theta)= -9/16, then what is theta?"

If so, we can use an identity.

cos (2*theta) = 2 cos²(theta) - 1

So, -9/16 = 2 cos²(theta) - 1 => 7/16 = 2 cos²(theta)

 

[Harry_the_cat]

Let 2 theta = A, then find A.
Once you have A, then find theta.
(Watch your domain!)

 

[Bob Brown MSEE]

WolframAlpha

Click Here

 

[stapel]

if cos 2 theta = -0.5625 how do i find theta?

To clarify one of the questions you received in response, is either one of the following the original equation?

. . . . .\(\displaystyle \mbox{a. }\, \cos(2 \theta)\, =\, -0.5625\)

. . . . .\(\displaystyle \mbox{b. }\, \cos^2(\theta)\, =\, -0.5625\)

Also, please do let us know if you've learned anything about inverse trig functions, or if you've only learned about the trig functions; and also if you're using a calculator or if you're having to work from tables. Thank you!