\[\begin{array}{l}b]\;\;\sqrt[3]{{125}} - \sqrt[3]{{54}}.\sqrt[3]{4}\\ = \sqrt[3]{{{5^3}}} - \sqrt[3]{{54.4}}\\ = \sqrt[3]{{{5^3}}} - \sqrt[3]{{216}}\\ = 5 - \sqrt[3]{{{6^3}}} = 5 - 6 = - 1.\end{array}\]
Đề bài
Tính :
a] \[\sqrt[3]{{125}} - \sqrt[3]{8} - 2\sqrt[3]{{27}}\];
b] \[\sqrt[3]{{125}} - \sqrt[3]{{54}}.\sqrt[3]{4}\].
Lời giải chi tiết
\[\begin{array}{l}a]\;\;\sqrt[3]{{125}} - \sqrt[3]{8} - 2\sqrt[3]{{27}}\\ = \sqrt[3]{{{5^3}}} - \sqrt[3]{{{2^3}}} - 2\sqrt[3]{{{3^3}}}\\ = 5 - 2 - 2.3\\ = - 3.\end{array}\]
\[\begin{array}{l}b]\;\;\sqrt[3]{{125}} - \sqrt[3]{{54}}.\sqrt[3]{4}\\ = \sqrt[3]{{{5^3}}} - \sqrt[3]{{54.4}}\\ = \sqrt[3]{{{5^3}}} - \sqrt[3]{{216}}\\ = 5 - \sqrt[3]{{{6^3}}} = 5 - 6 = - 1.\end{array}\]