b) (x – *)^2 = x^2 – 8ax + 16a^2;
b) (x – *)2 = x2 – 8ax + 16a2;
b) x2 – 8ax + 16a2 = x2 ‒ 2.x.4a + (4a)2 = (x ‒ 4a)2.
Vậy dấu * thay bằng 4a.