12+2m/3-7n = 0;
5m/3 = 15;
m = 9;
n = 18/7;
2 、( x-8)(x+2)=0
X=8 or x =-2;
(3x-5)(x+ 1)= 0;
X=5/3 or x =-1;
(3x- 1-7)(3x- 1+2)= 0;
(3x-8)(3x+ 1)= 0;
X=8/3 or x =-1/3;
(x+3a)(x-a)= 0;
X=-3a or x = a.