# trig

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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
= 0.00523599..

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

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

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