b) $\sqrt{8}$ (lấy k = 3).

b) Với p = 8 thì $\sqrt{8}$ ≈ 2,82843. Nếu ta chọn u₁ = 3 thì ta có:

u₁ = 3

$u_2=\frac{1}{2}\left(u_1+\frac{8}{u_1}\right)=\frac{1}{2}\left(3+\frac{8}{3}\right)$≈ 2,8333

$u_3=\frac{1}{2}\left(u_2+\frac{8}{u_2}\right)=\frac{1}{2}\left(2,8333+\frac{8}{2,3333}\right)$≈ 2,8284

$u_4=\frac{1}{2}\left(u_3+\frac{8}{u_3}\right)=\frac{1}{2}\left(2,8284+\frac{8}{2,8284}\right)$≈ 2,8284

$u_5=\frac{1}{2}\left(u_4+\frac{8}{u_4}\right)=\frac{1}{2}\left(2,8284+\frac{5}{2,8284}\right)$≈ 2,8284

Sai số tuyệt đối xấp xỉ bằng 2,8284 – 2,82843 = 0,00003.