* Bạn tham khảo nha >v< *
$\begin{align} & \dfrac{\sin {{40}^{o}}-\sin {{45}^{o}}+\sin {{50}^{o}}}{\cos {{40}^{o}}-\cos {{45}^{o}}+\cos {{50}^{o}}}-\dfrac{6\left( \sqrt{3}+3\tan {{15}^{o}} \right)}{3-\sqrt{3}\tan {{15}^{o}}} \\ & =\dfrac{\left( \sin {{40}^{o}}+\sin {{50}^{o}} \right)-\sin {{45}^{o}}}{\left( \cos {{40}^{o}}+\cos {{50}^{o}} \right)-\cos {{45}^{o}}}-\dfrac{6\left( \dfrac{\sqrt{3}}{3}+\tan {{15}^{o}} \right)}{1-\dfrac{1}{\sqrt{3}}\tan {{15}^{o}}} \\ & =\dfrac{2\sin {{45}^{o}}\cos {{5}^{o}}-\sin {{45}^{o}}}{2\cos {{45}^{o}}\sin {{5}^{o}}-\cos {{45}^{o}}}-\dfrac{6\left( \tan {{30}^{o}}+\tan {{15}^{o}} \right)}{1-\tan {{30}^{o}}\tan {{15}^{o}}} \\ & =\dfrac{\sin {{45}^{o}}}{\cos {{45}^{o}}}-6\tan \left( {{30}^{o}}+{{15}^{o}} \right) \\ & =\tan {{45}^{o}}-6\tan {{45}^{o}}=-5\tan {{45}^{o}}=-5 \\ \end{align}$
