$\sin a\cos a=\dfrac{12}{25}$
$\Leftrightarrow 1+2\sin a\cos a=\dfrac{49}{25}$
$\Leftrightarrow (\sin a+\cos a)^2=\dfrac{49}{25}$
$\Leftrightarrow \sin a+\cos a=\pm\dfrac{7}{5}$
+ Nếu $\sin a+\cos a=\dfrac{7}{5}$
$\Rightarrow \Big(\sin a;\cos a\Big)=\Big(\dfrac{4}{5}; \dfrac{3}{5}\Big), \Big(\dfrac{3}{5}; \dfrac{4}{5}\Big)$
+ Nếu $\sin a+\cos a=\dfrac{-7}{5}$
$\Rightarrow \Big(\sin a;\cos a\Big)=\Big(\dfrac{-4}{5}; \dfrac{-3}{5}\Big), \Big(\dfrac{-3}{5}; \dfrac{-4}{5}\Big)$
