3(Ⅹ十2、1)=10、5解：x+2.1=10.5÷3 x+2.1=3.5 x=3.5-2.1 x=1.4检验：左边=3x(1.4+2.1) =3x3.5 =10.5 =右边
3(x+2.1)=10.53x+6.3=10.53x=4.2x=1.4
