Saturday

November 22, 2014

November 22, 2014

Posted by **ody** on Wednesday, May 28, 2008 at 9:38pm.

- trig -
**drwls**, Wednesday, May 28, 2008 at 11:10pmSince 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 6:16amI 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 2:49pmThe 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...