[tex]1+\frac{1}{tg^2\alpha}=1+\frac{cos^2\alpha}{sin^2\alpha}=\frac{sin^2\alpha}{sin^2\alpha}+\frac{cos^2\alpha}{sin^2\alpha}=\frac{sin^2\alpha+cos^2\alpha}{sin^2\alpha}=\frac{1}{sin^2\alpha}[/tex]
Odp.: A
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