(x2 - 25)2 - (x - 5)2 = 0
<=> (x2 - 25 + x - 5)(x2 - 25 - x + 5) = 0
<=> (x2 + x - 30)(x2 - x - 20) = 0
<=> (x2 + 6x - 5x - 30)(x2 + 4x - 5x - 20) = 0
<=> [x(x + 6) - 5(x + 6)].[x(x + 4) - 5(x + 4)] = 0
<=> (x + 6)(x + 4)(x - 5)2 = 0
<=> x = -6 hoặc x = -4 hoặc x = 5