a) 2x - ( 40 - 52 ) = x + 12
2x - 40 + 52 = x + 12
x = 0
b) 40 - x =-12 + 3x
4x = 52
x = 13
a) 2x - ( 40 - 52 ) = x + 12
2x - 40 + 52 = x + 12
x = 0
b) 40 - x =-12 + 3x
4x = 52
x = 13
\(x-\left(21-x\right)=x+9\)
\(\Leftrightarrow x-21+x-x=9\)
\(\Leftrightarrow x=9 +21=30\)
\(x-\left(21-x\right)=x+9\)
\(\Leftrightarrow x-21+x=x+9\Leftrightarrow2x-21=x+9\)
\(\Leftrightarrow2x-x=9+21\Leftrightarrow x=30\)