Sunday

April 20, 2014

April 20, 2014

Posted by **Mandy** on Monday, May 3, 2010 at 2:07pm.

Determine all solutions of the equations in radians.

Find cos x/2, given that cos x = 1/4 and x terminates in 0 < x < π/2.

- trig -
**Reiny**, Monday, May 3, 2010 at 3:52pmlet's use

cos 2A = 2cos^2 A - 1

or

cos x = 2cos^2(x/2) - 1

1/4 = 2cos^2(x/2) - 1

5/8 = cos^2(x/2)

cosx = √5/√8 or √10/4

- For Reiny -
**Mandy**, Monday, May 3, 2010 at 4:11pmHow did you get 5/8? Thanks for your help!

- For Reiny -
**Mandy**, Monday, May 3, 2010 at 4:34pmHow did you get 5/8? Thanks for your help!

- trig -
**Reiny**, Monday, May 3, 2010 at 4:37pmfrom

1/4 = 2cos^2(x/2) - 1

1/ 4 + 1 = 2cos^2(x/2)

5/4 = 2cos^2(x/2) , now divide by 2

5/8 = cos^2(x/2) , now take √

cos x/2 = √5/√8 , rationalizing

cos x/2 = (√5/√8)(√8/√8) = √40/8 = 2√10/8 = √10/4

**Related Questions**

trig - hi, I have a placement test coming up tomorrow, and I'm pretty confident ...

Physics - Please help!!! Physics test!? I have a physics test tomorrow on ...

math help, test tomorrow!!! - For 0 <or equal B <or equal 2 pi determine ...

Trigonometry - I have some trigonometric equations to do, but I'm pretty lost, ...

Math ; please please help. - 1. Explain in detail how to determine the value of ...

trig - I'm confused with this concept: Okay, so I have this problem: cos2x( 2 ...

Please help for my test CALculus - using the chain rule find the min and max ...

solving trig. equations - tan(3x) + 1 = sec(3x) Thanks, pretend 3x equals x so ...

trig - I need to find all solutions of the given equations for the indicated ...

Algebra II- please help! - I just cannot seem to be able to grasp the concept of...