bài 69 Hãy tính (SGK)
1/ \(\sqrt[3]{512}=8\)
2/ \(\sqrt[3]{-729}=-9\)
3/ \(\sqrt[3]{0,064}=0,4\)
4/ \(\sqrt[3]{-0,216}=0,6\)
5/ \(\sqrt[3]{-0,008}=-0,2\)
Bài 68 Tính
1/ \(\sqrt[3]{27}-\sqrt[3]{-8}-\sqrt[3]{125}\)
=\(\sqrt[3]{3^3}-\sqrt[3]{-2^3}-\sqrt[3]{-5^3}\)
=\(3+2-5=0\)
2/ \(\frac{\sqrt[3]{135}}{\sqrt[3]{5}}-\sqrt[3]{54}.\sqrt[3]{4}\)
=\(\frac{\sqrt[3]{135}}{\sqrt[3]{5}}-\sqrt[3]{216}\)
=\(\sqrt[3]{27}-\sqrt[3]{6^3}=3-6=-3\)
Bài 69 So sánh
1/ 5 và \(\sqrt[3]{123}\)
ta có: \(5=\sqrt[3]{125}\)
\(125>123\)
Nên \(\sqrt[3]{125}>\sqrt[3]{123}\)
Vậy \(5>\sqrt[3]{123}\)
2/\(5\sqrt[3]{6}\) và \(6\sqrt[3]{5}\)
ta có: \(5\sqrt[3]{6}=\sqrt[3]{750}\)
\(6\sqrt[3]{5}=\sqrt[3]{1080}\)
=> 750 < 1080
Nên \(\sqrt[3]{750}< \sqrt[3]{1080}\)
Vậy \(5\sqrt[3]{6}< 6\sqrt[3]{5}\)
giúp mk vs