Đáp án:
$\begin{array}{l}
a + b = 10;a.b = 4\\
a){\left( {a - b} \right)^2}\\
= {a^2} - 2ab + {b^2}\\
= {a^2} + 2ab + {b^2} - 4ab\\
= {\left( {a + b} \right)^2} - 4ab\\
= {10^2} - 4.4\\
= 100 - 16\\
= 84\\
b){a^3} - {b^3}\\
= \left( {a - b} \right)\left( {{a^2} + ab + {b^2}} \right)\\
= \sqrt {{{\left( {a - b} \right)}^2}} .\left[ {{{\left( {a + b} \right)}^2} - ab} \right]\\
= \sqrt {84} .\left( {{{10}^2} - 4} \right)\\
= 2\sqrt {21} .96\\
= 192\sqrt {21} \\
c){a^4} + {b^4}\\
= {\left( {{a^2} + {b^2}} \right)^2} - 2{a^2}{b^2}\\
= \left[ {{{\left( {a + b} \right)}^2} - 2ab} \right] - 2.{\left( {ab} \right)^2}\\
= \left( {{{10}^2} - 2.4} \right) - {2.4^2}\\
= 100 - 8 - 2.16\\
= 60
\end{array}$
