tan(9)-tan27-tan63+tan81
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(tan9+tan81)−(tan63+tan27)(tan9+tan81)−(tan63+tan27)
Now (tanA+tanB=Sin(A+B)/CosAcosB)(tanA+tanB=Sin(A+B)/CosAcosB)
=Sin90/cos81cos9−sin90/cos63cos27=Sin90/cos81cos9−sin90/cos63cos27
=2/2cos81cos9−2/2cos63cos27=2/2cos81cos9−2/2cos63cos27
=2/cos72−2/cos36=2/cos72−2/cos36
=2(cos36−cos72/cos36cos73)2(cos36−cos72/cos36cos73)
=2(2sin54sin18/sin54sin18)=2(2sin54sin18/sin54sin18)
=4
Now (tanA+tanB=Sin(A+B)/CosAcosB)(tanA+tanB=Sin(A+B)/CosAcosB)
=Sin90/cos81cos9−sin90/cos63cos27=Sin90/cos81cos9−sin90/cos63cos27
=2/2cos81cos9−2/2cos63cos27=2/2cos81cos9−2/2cos63cos27
=2/cos72−2/cos36=2/cos72−2/cos36
=2(cos36−cos72/cos36cos73)2(cos36−cos72/cos36cos73)
=2(2sin54sin18/sin54sin18)=2(2sin54sin18/sin54sin18)
=4
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