Question

Giải giúp

Answer 1

a: \(A=\left(\sqrt[3]{49}+\sqrt[3]{4}-\sqrt[3]{14}\right)\left(\sqrt[3]{7}+\sqrt[3]{2}\right)\)

\(=\left(\sqrt[3]{7}+\sqrt[3]{2}\right)\left(\sqrt[3]{49}-\sqrt[3]{7\cdot2}+\sqrt[3]{4}\right)=\left(\sqrt[3]{7}\right)^3+\left(\sqrt[3]{2}\right)^3\)

=7+2

=9

c: \(C=\sqrt[3]{2+\sqrt5}+\sqrt[3]{2-\sqrt5}\)

=>\(C^3=2+\sqrt5+2-\sqrt5+3\cdot C\cdot\sqrt[3]{\left(2+\sqrt5\right)\left(2-\sqrt5\right)}=4-3C\)

=>\(C^3+3C-4=0\)

=>\(C^3-C^2+C^2-C+4C-4=0\)

=>(C-1)(C^2+C+4)=0

=>C-1=0

=>C=1