Posted by ody on Wednesday, May 28, 2008 at 9:38pm.
find the value of : sin18'

trig  drwls, Wednesday, May 28, 2008 at 11:10pm
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  Reiny, Thursday, May 29, 2008 at 6:16am
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  drwls, Thursday, May 29, 2008 at 2:49pm
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
Answer This Question
Related Questions
 trig identities  cos94 degrees cos18 degrees+ sin94 degrees sin18 degrees. ...
 trig  use the unit circle to find the exact value for all the trig functions of...
 trig  if (12,5) is a pointon the terminal side of an angel 0 find the exact ...
 trig  find each value by referring to the graphs of the trig functions. 1. sec ...
 trig  For the following expression, find the value of y that corresponds to ...
 trig/pre calc  hello, i don't quite understand how to do this type of problem...
 trig  please help me. use trig. identities to find the exact value. tan 25° + ...
 trig  please help me. use trig. identities to find the exact value. tan 25° + ...
 trig  what is the exact value of 7pi for all trig func.?
 trig  FInd the exact value pf the 6 trig function of alpha Given: point (2,6...
More Related Questions