a, (9.x-21) : 3 = 2
=>9x-21=6
=>9x=27
=>x=3
b, (x-39)-21=0
=>x-39-21=0
=>x-60=0
=>x=60
c, 231+(312-x)=531
=>231+312-x=531
=>543-x=531
=>x=543-531
=>x=12
d, 53.(9-x)=53
=>9-x=1
=>x=8
a/ \(\frac{\left(9x-21\right)}{3}=2\)
\(\Rightarrow9x-21=2\cdot3=6\)
\(\Rightarrow9x=6+21=27\)
\(\Rightarrow x=\frac{27}{9}=3\)
b/ \(\left(x-39\right)-21=0\)
\(\Rightarrow x-39=0+21=21\)
\(\Rightarrow x=21+39=60\)
c/ \(231+\left(312-x\right)=531\)
\(\Rightarrow312-x=531-231=300\)
\(\Rightarrow x=312-300=12\)
d/ \(53\cdot\left(9-x\right)=53\)
\(\Rightarrow9-x=\frac{53}{53}=1\)
\(\Rightarrow x=9-1=8\)
a) ( 9 . x - 21 ) : 3 = 2
9 . x - 21 = 6
9 . x = 6 + 21
9 . x = 27
x = 27 : 9
x = 3
b) ( x - 39 ) - 21 = 0
x - 39 = 21
x = 21 + 39
x = 60
c) 231 + ( 312 - x ) = 531
312 - x = 531 - 231
312 - x = 300
x = 312 - 300
x = 12
d) 53 . ( 9 - x ) = 53
9 - x = 1
x = 9 - 1
x = 8
