Algebra II

1) Find the exact value of cos 105 degrees by using a half-angle formula.

2)Find the solution of sin 2theta = cos theta if 0 degrees</= theta < 180 degrees.

I have read the book and looked at the examples, but cannot figure out how to work these. Any help would be great!!

Thanks

  1. 👍 0
  2. 👎 0
  3. 👁 106
asked by Lucy
  1. 1)
    105 * 2 = 210 is a nice angle, 180 + 30

    2)
    2 sin t cos t = cos t
    2 sin t = 1
    sin t = 1/2
    t = 30 degrees or pi/6 radians

    the other solution t = 150 degrees is no good because the cos t would be negative

    1. 👍 0
    2. 👎 0
    posted by Damon

Respond to this Question

First Name

Your Response

Similar Questions

  1. MATH

    1.)Find the exact solution algebriacally, if possible: (PLEASE SHOW ALL STEPS) sin 2x - sin x = 0 2.) GIVEN: sin u = 3/5, 0 < u < ï/2 Find the exact values of: sin 2u, cos 2u and tan 2u using the double-angle formulas. 3.)Use the

    asked by MAKITA on April 10, 2009
  2. Trig(3 all with work)

    1)Find the exact value of cos 105 by using a half-angle formula. A)sqrt 2 - sqrt 3 /2 B)-sqrt 2 - sqrt 3 /2 C)-sqrt 2 + sqrt 3 /2 D)sqrt 2 + sqrt 3 /2 cos 105 cos 105 = cos 210/2 sqrt 1 + 210/2 sqrt 1 + sqrt 3/2 /2 sqrt 2 + sqrt

    asked by Jon on February 15, 2008
  3. Algebra II

    Multiple Choice (theta) means the symbol 0 with the dash in it. 1.)Which expression is equivalent to tan(theta)-(sec(theta))/(sin(theta))? A.)-cot(theta) B.)cot(theta) C.)tan(theta)-cot(theta) D.)tan(theta)-sec^2(theta) 2.)Find

    asked by HotMath on June 9, 2011
  4. Please help Math

    a. Use the formulas for lowering powers to rewrite the expression in terms of the first power of cosine: (cos^4)x (or cos*x to the 4th power) b.Use an appropriate Half- Angle Formula to Find the Exact value of the expression: 1.

    asked by Tricia on March 3, 2014
  5. Mathmatics

    a. Use the formulas for lowering powers to rewrite the expression in terms of the first power of cosine: (cos^4)x (or cos*x to the 4th power) b.Use an appropriate Half- Angle Formula to Find the Exact value of the expression: 1.

    asked by Tricia on March 3, 2014
  6. Trig

    If angle A is 45 degrees and angle B is 60 degrees. Find sin(A)cos(B), find cos(A)sin(B), find sin(A)sin(B), and find cos(A)cos(B) The choises for the first are: A. 1/2[sin(105)+sin(345)] B. 1/2[sin(105)-sin(345)] C.

    asked by Sade on October 8, 2016
  7. math

    Use the appropriate sum/difference formula to find the exact value of cos(105°). do we choose one, then make 1 side equal cos of 105°? I don't understand the question.

    asked by Anonymous on April 15, 2012
  8. Trigonometry

    use the appropriate trig identity (sum and difference, half angle, double angle) to find the exact value. 1)cos 255 degrees 2) sin 165 degrees 3) tan 285 degrees

    asked by Jennifer on March 3, 2011
  9. trig

    use a half-angle identity to find the exact value of tan 105 degrees.

    asked by Karen on July 22, 2013
  10. Trigonometry - Identities

    If tan 2x = - 24/7, where 90 degrees < x < 180 degrees, then find the value of sin x+ cos x. I applied various identities and tried manipulating the problem to get sin x + cos x = sin(arctan(-24/7)/2) + cos(arctan(-24/7)/2) I also

    asked by Sam on November 14, 2013

More Similar Questions