A.\(\dfrac{{a + b}}{2} > \sqrt {ab} \) với \(a,\,\,b \ge 0\)
B.\({\left( {\dfrac{{a + b}}{2}} \right)^2} \ge \dfrac{{{a^2} + {b^2}}}{2}\)
C.\({a^2} + {b^2} + 1 \ge a + b + ab\)
D.\({a^2} + {b^2} + 9 > 3\left( {a + b} \right) + ab\)

A.\(2 < \dfrac{{a + b}}{{a + b + c}} + \dfrac{{b + c}}{{b + c + d}} + \dfrac{{c + d}}{{c + d + a}} + \dfrac{{d + a}}{{d + a + b}} < \dfrac{5}{2}\)
B.\(2 < \dfrac{{a + b}}{{a + b + c}} + \dfrac{{b + c}}{{b + c + d}} + \dfrac{{c + d}}{{c + d + a}} + \dfrac{{d + a}}{{d + a + b}} < 4\)
C.\(2 < \dfrac{{a + b}}{{a + b + c}} + \dfrac{{b + c}}{{b + c + d}} + \dfrac{{c + d}}{{c + d + a}} + \dfrac{{d + a}}{{d + a + b}} < 5\)
D.\(2 < \dfrac{{a + b}}{{a + b + c}} + \dfrac{{b + c}}{{b + c + d}} + \dfrac{{c + d}}{{c + d + a}} + \dfrac{{d + a}}{{d + a + b}} < 3\)

A.\(x < y < z\)
B.\(y < x < z\)
C.\(z < x < y\)
D.\(x < z < y\)

A.\({\left( {a - \dfrac{b}{2}} \right)^2} + {\left( {a - \dfrac{c}{2}} \right)^2} + {\left( {a - \dfrac{d}{2}} \right)^2} + {\left( {a - \dfrac{e}{2}} \right)^2} \ge 0\)
B.\({\left( {b - \dfrac{a}{2}} \right)^2} + {\left( {c - \dfrac{a}{2}} \right)^2} + {\left( {d - \dfrac{a}{2}} \right)^2} + {\left( {e - \dfrac{a}{2}} \right)^2} \ge 0\)
C.\({\left( {b + \dfrac{a}{2}} \right)^2} + {\left( {c + \dfrac{a}{2}} \right)^2} + {\left( {d + \dfrac{a}{2}} \right)^2} + {\left( {e + \dfrac{a}{2}} \right)^2} \ge 0\)
D.\({\left( {a - b} \right)^2} + {\left( {a - c} \right)^2} + {\left( {a - d} \right)^2} + {\left( {a - e} \right)^2} \ge 0\)

A.\(\dfrac{{{a^4}{b^2} + {b^4}{c^2} + {c^4}{a^2} + 3}}{{{a^{2020}} + {b^{2020}} + {c^{2020}}}} \ge 1\)
B.\(\dfrac{{{a^4}{b^2} + {b^4}{c^2} + {c^4}{a^2} + 3}}{{{a^{2020}} + {b^{2020}} + {c^{2020}}}} \ge \dfrac{1}{2}\)
C.\(\dfrac{{{a^4}{b^2} + {b^4}{c^2} + {c^4}{a^2} + 3}}{{{a^{2020}} + {b^{2020}} + {c^{2020}}}} \ge 2\)
D.\(\dfrac{{{a^4}{b^2} + {b^4}{c^2} + {c^4}{a^2} + 3}}{{{a^{2020}} + {b^{2020}} + {c^{2020}}}} \ge \dfrac{3}{2}\)

A.\(11\)
B.\(12\)
C.\(13\)
D.\(14\)

A.một lần
B.hai lần
C.ba lần
D.bốn lần

A.>
B.<
C.=
D.Tất cả đều sai

A.\(\frac{{24}}{{19}} < \frac{{39}}{{34}}\)
B.\(\frac{{24}}{{19}} = \frac{{39}}{{34}}\)
C.\(\frac{{24}}{{19}} > \frac{{39}}{{34}}\)
D.Tất cả đều sai

A.=
B.>
C.<
D.Tất cả đều sai