Ta có: \(5\cdot7\cdot77-7\cdot60+49\cdot25-15\cdot42\)
\(=55\cdot49-7\cdot60+49\cdot25-7\cdot90\)
\(=\left(55\cdot49+25\cdot49\right)-\left(7\cdot60+7\cdot90\right)\)
\(=29\cdot\left(55+25\right)-7\cdot\left(60+90\right)\)
\(=29\cdot80-7\cdot150\)
\(=10\cdot\left(29\cdot8-7\cdot15\right)\)
\(=10\cdot\left(232-105\right)\)
\(=10\cdot127=1270\)