Cho a là góc nhọn biết sin a=3/5 Tính cos a, tan a, cot a

$\textit{Ta có:}$

$\sin^2 a$ + $\cos^2 a$ $\textit{=1}$

`<=>`$\cos^2 a$ $\textit{= 1 - $\sin^2$ a}$

$\Leftrightarrow$$\cos a $  $\textit{=}$ $\sqrt[]{1-\frac{9}{25}}$ $\textit{=}$ $\frac{4}{5}$

$\textit{Do a là góc nhọn $\Rightarrow$$\cos a$ = $\frac{4}{5}$}$

$\textit{$\tan a$=}$$\frac{\sin a}{\cos a}$ $\textit{= $\frac{3}{5}$:$\frac{4}{5}$ = $\frac{3}{4}$ }$

$\textit{$\cot a$=}$$\frac{\cos a}{\sin a}$ $\textit{= $\frac{4}{5}$:$\frac{3}{5}$ = $\frac{4}{3}$ }$