\(3\overrightarrow{MA}+2\overrightarrow{MB}-5\overrightarrow{MC}=3\left(\overrightarrow{MC}+\overrightarrow{CA}\right)+2\left(\overrightarrow{MC}+\overrightarrow{CB}\right)-5\overrightarrow{MC}\)
\(=3\overrightarrow{CA}+2\overrightarrow{CB}+5\overrightarrow{MC}-5\overrightarrow{MC}=3\overrightarrow{CA}+2\overrightarrow{CB}\)