a, x^2(x-3)-x+3=0
x^2(x-3)-(x-3)=0
(x^2-1)(x-3)=0
(x-1)(x+1)(x-3)=0
th1:x-1=0
x=1
th2:x+1=0
x=-1
th3:x-3=0
x=3
Vậy x=1 hoặc x=-1 hoặc x=1
b,(x^2+10x+25)-(x^2-8x+16)=0
x^2+10x+25-x^2+8x-16=0
(x^2-x^2)+(10x+8x)+(25-16)=0
18x+9=0
18x=-9
x=-1/2
Vậy x=-1/2