[tex]\bf tan(\theta)=\cfrac{sin(\theta)}{cos(\theta)}
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sin^2(\theta)+cos^2(\theta)=1\implies cos^2(\theta)=1-sin^2(\theta)\\\\
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\cfrac{tan(x)[1-sin^2(x)]}{2}\implies \cfrac{\frac{sin(x)}{cos(x)}\cdot cos^2(x)}{2}\implies \boxed{\cfrac{sin(x)cos(x)}{2}}[/tex]
