Đáp án:
$\begin{array}{l}
a){24^2} + {16^2} + 48.76\\
= {24^2} + 2.24.76 + {76^2}\\
= {\left( {24 + 76} \right)^2}\\
= {100^2}\\
= 10000\\
b){79^2} + {29^2} - 58.79\\
= {79^2} - 2.29.79 + {29^2}\\
= {\left( {79 - 29} \right)^2}\\
= {50^2}\\
= 2500\\
c)\left\{ \begin{array}{l}
x + y + z = 0 \Rightarrow x = - y - z\\
xy + yz + xz = 0
\end{array} \right.\\
\Rightarrow \left( { - y - z} \right).y + y.z + \left( { - y - z} \right).z = 0\\
\Rightarrow - {y^2} - yz + yz - yz - {z^2} = 0\\
\Rightarrow {y^2} + yz + {z^2} = 0\\
\Rightarrow {\left( {y + z} \right)^2} = y.z\\
\Rightarrow {\left( { - x} \right)^2} = y.z\\
\Rightarrow {x^2} = y.z\\
TT:\left\{ \begin{array}{l}
{y^2} = z.x\\
{z^2} = x.y
\end{array} \right.\\
\Rightarrow x = y = z
\end{array}$
