Ai Giúp Mình Với ạ!!!!!!!!!!!!!!!!!!!

Công thức áp dụng:

$\begin{array}{l}
\tan \left( {{{90}^o} - \alpha } \right) = \cot \alpha ,\tan \alpha \cot \alpha  = 1\\
\sin \left( {\dfrac{\pi }{2} - \alpha } \right) = \cos \alpha ,{\sin ^2}\alpha  + {\cos ^2}\alpha  = 1
\end{array}$

$\begin{array}{l}
C = {\sin ^2}{45^o} - 2{\sin ^2}{50^o} + 3{\cos ^2}{45^o} - 2{\sin ^2}{40^o} + 4\tan {55^o}.\tan {35^o}\\
C = \left( {{{\sin }^2}{{45}^o} + 3{{\cos }^2}{{45}^o}} \right) - 2\left( {{{\sin }^2}{{50}^o} + {{\sin }^2}{{40}^o}} \right) + 4\tan {55^o}.\cot {35^o}\\
C = 4{\sin ^2}{45^o} - 2\left( {{{\sin }^2}{{50}^o} + {{\cos }^2}{{50}^o}} \right) + 4\\
C = 4{\sin ^2}{45^o} - 2 + 4 = 4.{\left( {\dfrac{{\sqrt 2 }}{2}} \right)^2} - 2 + 4\\
 = 4.\dfrac{1}{2} - 2 + 4 = 4
\end{array}$