Question

if sin 18=root 5-1\4 then sin 81 =

Answer 1

Answer:

sin(18∘)=5–√−14.

We are required to find sin(81∘)=cos(90∘−81∘)=cos(9∘).

cos(18∘)=1−sin2(18∘)−−−−−−−−−−√=5+5–√8−−−−−−−√≈0.951056516

Now, cos2θ=2cos2θ−1.

Therefore, cosθ=12(1+cos2θ)−−−−−−−−−−−√.

Therefore, cos(9∘)=12(1+cos(18∘))−−−−−−−−−−−−−√=12(1+5+5–√8−−−−−−−√)−−−−−−−−−−−−−−−−⎷≈0.987688341

Step-by-step explanation:

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