A.\(\dfrac{{ - 2}}{{21}}\)
B.\(\dfrac{{20}}{9}\)
C.\(\dfrac{2}{{21}}\)
D.\(\dfrac{{ - 10}}{{21}}\)

A.\(P = 12\)
B.\(P = 14\)
C.\(P = 16\)
D.\(P = 18\)

A.\(90\,\,\,\left( {c{m^2}} \right)\)
B.\(90\pi \,\,\,\left( {c{m^2}} \right)\)
C.\(70\pi \,\,\,\left( {c{m^2}} \right)\)
D.\(70\,\,\,\left( {c{m^2}} \right)\)

A.\(\dfrac{1}{{{{\left( {a + b} \right)}^2}}}\)
B.\(\dfrac{1}{{{a^2} + {b^2}}}\)
C.\(\dfrac{1}{{{{\left( {a + b} \right)}^3}}}\)
D.\(\dfrac{1}{{{a^3} + {b^3}}}\)

A.\(-a\)
B.\(a\)
C.\(-b\)
D.\(b\)

A.\(\dfrac{{5 - \sqrt 7 }}{4}\) hoặc \(\dfrac{{5 + \sqrt 7 }}{4}\)
B.\(\dfrac{{5 - \sqrt 5 }}{7}\) hoặc \(\dfrac{{5 + \sqrt 5 }}{4}\)
C.\(\dfrac{{2 - \sqrt 3 }}{5}\) hoặc \(\dfrac{{2 + \sqrt 3 }}{5}\)
D.\(\dfrac{{3 - \sqrt 2 }}{5}\) hoặc \(\dfrac{{3 + \sqrt 2 }}{5}\)

A.\(\dfrac{{\sqrt {3 - 2{m^2} - {m^4}} }}{2}\)
B.\(\dfrac{{\sqrt {{m^4} - 2{m^2} - 3} }}{2}\)
C.\(\dfrac{{\sqrt {3 + 2{m^2} - {m^4}} }}{2}\)
D.\(\dfrac{{\sqrt {{m^4} + 2{m^2} + 3} }}{2}\)

A.\(A = 1\)
B.\(A = \dfrac{1}{4}\)
C.\(A = \dfrac{1}{{16}}\)
D.\(A = \dfrac{1}{9}\)

A.\({\left( {\tan x - \cot x} \right)^2} \ge 4\)
B.\({\left( {\tan x + \cot x} \right)^2} \ge 4\)
C.\({\left( {\tan x + \cot x} \right)^2} \le 2\)
D.\({\left( {\tan x + \cot x} \right)^2} \le 4\)

A.\(P = 1\)
B.\(P =  - 1\)
C.\(P =  - \sqrt 5 \)
D.\(P = \sqrt 5 \)