\[Дано:a = 12\ м;\ \ b = 16\ м;\ \ \]
\[P\left( \text{ABC} \right) = 48\ м.\ \]
\[Найти:c - ?\]
\[Решение:\]
\[1)\ P\left( \text{ABC} \right) = a + b + c =\]
\[= 12 + 16 + c > 48.\]
\[28 + c > 48\]
\[c > 48 - 28\]
\[c > 20\ м.\]
\[2)\ 16 + 12 > c \Longrightarrow 28 > c\]
\[3)\ 12 + c > 16 \Longrightarrow c > 4\]
\[20\ м < c < 28\ м.\]
\[Ответ:сторона\ c \Longrightarrow\]
\[\Longrightarrow 20\ м < c < 28\ м.\]