Commutativité: 2·3 =3·2 ; 2+3 =3+2; 2-3 =-3+2

Go ! $2+ab+3-ba = 2+3+ab-ab = 5$ $a^2b+aba $ =   $2xy+1-yx $ =   $(1+a)^2-(-1+a+2)^2) $ =   $b(1-a)+(a-1)b $ =   $2(1+a)-(a+1)(1+1^2) $ =