a) x^2(x^2+4) - 3x(x^2+1) + 1 = 0
<=> x^4 + 4x^2 - 3x^3 - 3x + 1 = 0
<=> x^4 - x^3 - 2x^3 + 2x^2 + 2x^2 - 2x - x + 1 = 0
<=> x^3(x-1) - 2x^2(x-1) + 2x(x-1) - (x-1) = 0
<=> (x-1) ( x^3-2x^2+2x-1 ) = 0
<=> (x-1) ( x^3 - x^2 - x^2 + x + x - 1 ) = 0
<=> (x-1)^2 . ( x^2 -x + 1 ) = 0
<=> x = 2
b) Ko có pt, viết lại đề.