[tex]a = 6y\\c = 6,5y\\b = ?\\cos\alpha = ?\\sin\alpha = ?\\\\\\Z \ tw. \ Pitagorasa:\\\\a^{2}+b^{2} = c^{2}\\\\(6y)^{2}+b^{2}=(6,5y)^{2}\\\\36y^{2}+b^{2} = 42,25y^{2}\\\\b^{2} = 42,25y^{2}-36y^{2} = 6,25y^{2}\\\\b = \sqrt{6,25y^{2}}\\\\b = 2,5y\\\\\\cos\alpha = \frac{b}{c} = \frac{2,5y}{6,5y} = \frac{2,5}{6,5}\\\\sin\alpha = \frac{a}{c} = \frac{6y}{6,y} = \frac{6}{6,5}[/tex]
[tex]\frac{3cos\alpha+sin\alpha}{13cos\alpha\cdot sin\alpha} = \frac{3\cdot\frac{2,5}{6,5}+\frac{2,5}{6,5}}{13\cdot\frac{2,5}{6,5}\cdot\frac{6}{6,5}}=\frac{\frac{7,5}{6,5}+\frac{6}{6,5}}{\frac{195}{6,5\cdot6,5}} =\frac{\frac{13,5}{6,5}}{\frac{195}{6,5\cdot6,5}} = \frac{13,5}{6,5}\cdot\frac{6,5\cdot6,5}{195} = \frac{87,75}{195} = 0,45[/tex]
