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basic trigonometry
(Tan^3θ-1)/Tanθ =Sec^2θ+Tanθ
R.H.S=Sec^2θ+Tanθ =(1/Cos^2θ) + (Sinθ/Cosθ) =(1+Cosθ.Sinθ)/Cos^2θ =(1/Cos^2θ) + (Cosθ.Sinθ)/Cos^2θ =Sec^2θ+(Sinθ/Cosθ) =Sec^2θ+Tanθ
Hence Proved
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