a) \(\left[\left(4x+28\right).3+55\right]:5=35\)
\(\Leftrightarrow\left(4x+28\right).3+55=35.5\)
\(\Leftrightarrow\left(4x+28\right).3+55=175\)
\(\Leftrightarrow\left(4x+28\right).3=175-55\)
\(\Leftrightarrow\left(4x+28\right).3=120\)
\(\Leftrightarrow4x+28=120:3\)
\(\Leftrightarrow4x+28=40\)
\(\Leftrightarrow4x=40-28\)
\(\Leftrightarrow4x=12\)
\(\Leftrightarrow x=12:4\)
\(\Leftrightarrow x=3\)
Vậy \(x=3\)
b) \(\left(12x-4^3\right).8^3=4.8^4\)
\(\Leftrightarrow12x-4^3=4.8^4:8^3\)
\(\Leftrightarrow12x-4^3=4.8^{4-3}\)
\(\Leftrightarrow12x-4^3=4.8\)
\(\Leftrightarrow12x-4^3=32\)
\(\Leftrightarrow12x-64=32\)
\(\Leftrightarrow12x=32+64\)
\(\Leftrightarrow12x=96\)
\(\Leftrightarrow x=96:12\)
\(\Leftrightarrow x=8\)
Vậy \(x=8\)
c) \(720:\left[41-\left(2x-5\right)\right]=2^3.5\)
\(\Leftrightarrow720:\left[41-\left(2x-5\right)\right]=8.5\)
\(\Leftrightarrow720:\left[41-\left(2x-5\right)\right]=40\)
\(\Leftrightarrow41-\left(2x-5\right)=720:40\)
\(\Leftrightarrow41-\left(2x-5\right)=18\)
\(\Leftrightarrow2x-5=41-18\)
\(\Leftrightarrow2x-5=23\)
\(\Leftrightarrow2x=23+5\)
\(\Leftrightarrow2x=28\)
\(\Leftrightarrow x=28:2\)
\(\Leftrightarrow x=14\)
Vậy \(x=14\)
