posted by .

find the value of : sin18'

  • trig -

    Since that is a very small angle, the radian approximation
    sin theta = theta (in radians)
    can be used.

    18' = 18/60 degree = 0.3000 degrees
    = 0/3*(pi/180)= pi/600 radians
    = 0.00523599..

    The true sine of the angle is very nearly the same. The exact value is 0.00523596..

  • trig -

    I have seen this question as :
    find the exact value of sin 18º

    18 = 1/2 of 36

    Start with a regular pentagon and draw several of the diagonals.

    You will see an abundance of angles of 36º,72º and 108º in similar triangles,
    and the diagonals intersect each other in the "golden ratio" which is (1+√5)/2

    using the cosine law we can show that
    cos 36º = (1+√5)/4 which is 1/2(golden ratio)

    cos 36º = 1 - 2sin^2 18º

    substituting and solving for sin 18º
    I got sin 18º = √[(3-√5)/8]

  • trig -

    The question still shows up as "18 minutes" on my (Mac) computer but the symbol for degrees appears in Reiny's answer. C'est la vie

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. trig/pre -calc

    hello, i don't quite understand how to do this type of problem: 1. find the exact value of sin (pi/3). even more confusing is 2. find the exact value of csc^-1 (1). i would appreciate any kind of help! thank you!
  2. trig

    find each value by referring to the graphs of the trig functions. 1. sec 4 pi...i got 0 Find the values for theta for which each equation is true. csc (theta)=1 i got pi over 2 +2 pi n
  3. trig

    use the unit circle to find the exact value for all the trig functions of è=2ð/3.
  4. trig

    what is the exact value of 7pi for all trig func.?
  5. trig

    please help me. use trig. identities to find the exact value. tan 25° + tan 5° / 1- tan 25° tan 5°
  6. trig

    please help me. use trig. identities to find the exact value. tan 25° + tan 5° / 1- tan 25° tan 5°
  7. trig identities

    cos94 degrees cos18 degrees+ sin94 degrees sin18 degrees. write the expression as the sine, cosine, or tangent of an angle.
  8. trig

    FInd the exact value pf the 6 trig function of alpha Given: point (-2,-6) on the terminal side of the angle in standard position sin alpha cos alpha tan alpha sec alpha csc alpha cot alpha
  9. trig

    For the following expression, find the value of y that corresponds to each value of x, then write your results as ordered pairs (x,y). y=7cos(x-pi/6) for x=pi/6, pi/3, 2pi/3, pi, 7pi/6
  10. trig

    if (-12,5) is a pointon the terminal side of an angel 0 find the exact value of six trig funcation of 0

More Similar Questions