若f(a)=(2tana)-[(2sin^2a/2 -1)/sin(a/2)cos(a/2)]则f(兀/12)=

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若f(a)=(2tana)-[(2sin^2a/2 -1)/sin(a/2)cos(a/2)]则f(兀/12)=
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若f(a)=(2tana)-[(2sin^2a/2 -1)/sin(a/2)cos(a/2)]则f(兀/12)=
若f(a)=(2tana)-[(2sin^2a/2 -1)/sin(a/2)cos(a/2)]则f(兀/12)=

若f(a)=(2tana)-[(2sin^2a/2 -1)/sin(a/2)cos(a/2)]则f(兀/12)=
由f(a)=(2tana)-[(2sin^2a/2 -1)/sin(a/2)cos(a/2)]
先对f(a)进行化简
f(a)=(2tana)-[-2(1-2sin^2a/2 )/2sin(a/2)cos(a/2)]
=(2tana)+2cosa/sina
=2(sina/cosa+cosa/sina)
=2[(sin^2a+cos^2a)/sinacosa]
=2/sinacosa
=4/sin2a
所以f(π/12)=4/sin2π/12=8