[b] ABC is a right-angled triangle at \( C, A C=6 \mathrm{~cm} ., \mathrm{BC}=8 \), Find: 1 ) \( \cos A \cos B-\sin A \sin B \) (a) \( m(\angle B) \)

15. Simplifa cada erpresion a) \( \operatorname{sen} \alpha \cdot \cot \alpha \) b) \( \tan \alpha+\cot \alpha \) c) \( \operatorname{sen} \alpha \cdot(\tan \alpha+\cot \alpha) \) 16. Demuestra las siguientes identidades

[b] ABC is a right-angled triangle at \( C, A C=6 \mathrm{~cm} ., \mathrm{BC}=8 \), Find: 1 ) \( \cos A \cos B-\sin A \sin B \) (a) \( m(\angle B) \)

15. Simplifica cada expresión. a) \( \operatorname{sen} \alpha \cdot \cot \alpha \) b) \( \tan \alpha+\cot \alpha \) c) \( \operatorname{sen} \alpha \cdot(\tan \alpha+\cot \alpha) \)

3. Given that \( \sin \beta=\frac{6}{7} \), where \( 0^{\circ} \leq \beta \leq 90^{\circ} \), find \( \tan \beta \).

Ao transtormar o arco de medida \( 12^{\circ} \) em radianos e o arco de medida de \( \frac{\pi}{9} \) radianos em graus, obtemos os arcos, respectivamente: