Đáp án:
$\begin{array}{l}
a)\\
A = {\sin ^6}x + 3{\sin ^4}x.{\cos ^2}x + 3{\sin ^2}x.{\cos ^4}x + {\cos ^6}x\\
= {\left( {{{\sin }^2}x + {{\cos }^2}x} \right)^3}\\
= {1^3}\\
= 1\\
b)\\
B = \left( {1 + \cos a} \right)\left( {1 - \cos a} \right) - {\sin ^2}a\\
= 1 - {\cos ^2}a - {\sin ^2}a\\
= 1 - \left( {{{\cos }^2}a + {{\sin }^2}a} \right)\\
= 1 - 1\\
= 0
\end{array}$
