第11章 11.3

(1)

$\sin\alpha = \frac{5}{13}$

$\cos\alpha = \frac{\sqrt{13^2-5^2}}{13} = \frac{12}{13}$

$\tan\alpha = \frac{\sin\alpha}{\cos\alpha} = \frac{5}{12}$

(2)

$\tan\alpha = \frac{3}{4}$

$\sin\alpha = \frac{3}{\sqrt{3^2+4^2}} = \frac{3}{5}$

$\cos\alpha = \frac{4}{5}$