计算arccos(sin 3π/5)的值

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计算arccos(sin3π/5)的值计算arccos(sin3π/5)的值计算arccos(sin3π/5)的值设a=arccos(sin3π/5)cosa=cosarccos(sin3π/5)=s

计算arccos(sin 3π/5)的值
计算arccos(sin 3π/5)的值

计算arccos(sin 3π/5)的值
设a=arccos(sin 3π/5)
cosa=cosarccos(sin 3π/5)=sin3π/5=cos(π/2-3π/5)=cos(-π/10)=cosπ/10
所以a=π/10

令 a=arccos(3/5) cos(a)=3/5 所以sin(a)=4/5
所以 sin(2a)=2sin(a)*cos(a)=2*3/5*4/5=24/25