2x - 7 = 20 + 5.(-3)
=> 2x - 7 = 20 - 15
=> 2x = 5 + 7
=> 2x = 12
=> x = 12 : 2
=> x = 6
\(2x-7=20+5.\left(-3\right)\)
\(\Leftrightarrow2x-7=20+\left(-15\right)\)
\(\Leftrightarrow2x-7=5\)
\(\Leftrightarrow2x=12\Leftrightarrow x=6\)
\(2x-7=20+5.\left(-3\right)\)
\(\Leftrightarrow2x-7=20-15\)
\(\Leftrightarrow2x-7=5\)
\(\Leftrightarrow2x=5+7\)
\(\Leftrightarrow2x=12\)
\(\Leftrightarrow x=12\div2\)
\(\Leftrightarrow x=6\)
Vậy x = 5