231 + ( 321 - x ) = 531
⇔ 321 - x = 531 - 231
⇔ 321 - x = 300
⇔ x = 300 + 321
⇔ x = 621
Vậy , x = 621
-------------------------------------
131.x - 941 = 2^7 . 2^3
⇔ 131.x - 941 = 2^10
⇔ 131.x - 941 = 1024
⇔ 131.x = 1024 + 941
⇔ 131.x = 1965
⇔ x = 1965 : 131
⇔ x = 15
Vậy , x = 15
---------------------------
( 4x+5 )/3 - 121/11 = 4
⇔ ( 4x+5 ): 3 - 11 = 4
⇔ ( 4x+5 ) : 3 = 4 + 11
⇔ ( 4x+5 ) : 3 = 15
⇔ 4x+5 = 15 x 3
⇔ 4x + 5 = 45
⇔ 4x = 45 - 5
⇔ 4x = 40
⇔ x = 40 : 4
⇔ x = 10
Vậy , x = 10
