B = $\sqrt[2]{x - 1 - 2\sqrt[2]{x - 2}}$ + 1 + $\sqrt[2]{x - 2}$ với 2 ≤ x < 3
= $\sqrt[2]{x - 2\sqrt[2]{x - 2} - 1}$ + 1 + $\sqrt[2]{x - 2}$
= $\sqrt[2]{x - 2 - 2\sqrt[2]{x - 2} - 1 + 2}$ + 1 + $\sqrt[2]{x - 2}$
= $\sqrt[2]{(x - 2) - 2\sqrt[2]{x - 2} + 1}$ + 1 + $\sqrt[2]{x - 2}$
= $\sqrt[2]{(\sqrt[2]{x - 2} - 1)² }$ + 1 + $\sqrt[2]{x - 2}$
= |$\sqrt[2]{x - 2}$ - 1| + 1 + $\sqrt[2]{x - 2}$ (*)
Có: 2 ≤ x < 3
⇔ 2 - 2 ≤ x - 2 < 3 - 2
⇔ 0 ≤ x - 2 < 1
⇔ 0 ≤ $\sqrt[2]{x - 2}$ < 1
⇔ 0 - 1 ≤ $\sqrt[2]{x - 2}$ - 1 < 1 - 1
⇔ -1 ≤ $\sqrt[2]{x - 2}$ - 1 < 0
⇒$\sqrt[2]{x - 2}$ - 1 nhận giá trị âm với 2 ≤ x < 3
(*)= 1 - $\sqrt[2]{x - 2}$ + 1 + $\sqrt[2]{x - 2}$
= 2
