Ta có:

$\left\{ \begin{align} & |15-a|\ge 0,\,\,\,\forall a \\ & {{\left( b-18 \right)}^{2}}\ge 0,\,\,\,\forall b \\ \end{align} \right.$

Do đó |15 – a| + ${{\left( b-18 \right)}^{2}}\le 0$ suy ra:

|15 – a| + ${{\left( b-18 \right)}^{2}}=0$

$\Rightarrow \left\{ \begin{align} & |15-a|=0 \\  & {{\left( b-18 \right)}^{2}}=0\\\end{align} \right.$

$\Rightarrow $ a = 15 và b = 18