Đáp án:
$\begin{array}{l}
C = {a^4} + {b^4}\\
= {a^4} + 2{a^2}.{b^2} + {b^4} - 2{a^2}{b^2}\\
= {\left( {{a^2} + {b^2}} \right)^2} - 2{a^2}{b^2}\\
= {\left( {{a^2} + 2ab + {b^2} - 2ab} \right)^2} - 2{a^2}{b^2}\\
= {\left[ {{{\left( {a + b} \right)}^2} - 2ab} \right]^2} - 2{a^2}{b^2}\\
= {\left( {{S^2} - 2P} \right)^2} - 2{S^2}
\end{array}$