precalculus
posted by ama .
write each expression as the sine, cosine or tangent of a double angle. then find the exact value of the expression.
a. 2sin 22.5 cos 22.5
b. cos^2 105 sin^2 105

precalculus 
Damon
a, use
sin 45 = cos 45 = 1/sqrt 2
b, use
105 = (1/2) 210 which is 180 + 30
so use
sin 210 = 1/2
cos 210 = sqrt 3/2
Respond to this Question
Similar Questions

trig
Reduce the following to the sine or cosine of one angle: (i) sin145*cos75  cos145*sin75 (ii) cos35*cos15  sin35*sin15 Use the formulae: sin(a+b)= sin(a) cos(b) + cos(a)sin(b) and cos(a+b)= cos(a)cos(b)  sin(a)sin)(b) (1)The quantity … 
Math 2nd question
Express as a single sine or cosine function (note: this is using double angle formulas) g) 8sin^2x4 I just don't get this one. I know it's got something to do with the 12sin^2x double angle formula. It's the opposite though? 
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 doubleangle formulas. 3.)Use … 
Math Trig
1. Determine the exact value of cos^1 (pi/2). Give number and explanaton. 2. Determine the exact value of tan^1(sq. root 3). with explanation. 3. Determine exact value of cos(cos^1(19 pi)). with explanation. 4. Determine the exact … 
precalculus
Write each expression as sine, cosine, or tangent of an angle. Then find the exact value of the expression tan 50tan20/1+ tan 50 tan20 
trig
Write the expression as the sine, cosine, or tangent of a double angle. Then find the exact value of the expression. 2tan 2pi/3 / 1tan^2 2pu/3 
PreCalc
1) Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one number. cos 12° cos 18° − sin 12° sin 18° And Find its exact value. 2) Use an Addition or Subtraction Formula to write the … 
PreCalc
I am really struggling with how to do these problems, I posted them a few minutes ago but the answers/work shown was incorrect. 1) a) Use an Addition or Subtraction Formula to write the expression as a trigonometric function of one … 
Math
Write the expression as the sine, cosine, or tangent of an angle. cos 0.96 cos 0.42 + sin 0.96 sin 0.42 Is this cos 0.54? 
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. 1/2[sin(345)+cos(105)] …