[tex]\frac{8sin\alpha-cos\alpha}{7sin\alpha+cos\alpha}=\frac{\frac{8sin\alpha}{sin\alpha}-\frac{cos\alpha}{sin\alpha}}{\frac{7sin\alpha}{sin\alpha}+\frac{cos\alpha}{sin\alpha}}=\frac{8-ctg\alpha}{7+ctg\alpha}=\frac{8-5}{7+5}=\frac{3}{12}=\frac{1}{4}[/tex]
