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.\(P = \sqrt 5 \)

A.\(2x\sqrt {1 + {x^2}} \)
B.\(\dfrac{{1 - {x^2}}}{{1 + {x^2}}}\)
C.\(\dfrac{{2x}}{{1 - {x^2}}}\)
D.\(\dfrac{{2x}}{{1 + {x^2}}}\)

A.\(1\)
B.\(2\)
C.\(3\)
D.\(4\)

A.1
B.2
C.3
D.4

A.75,1.
B.85,5.
C.84,7.
D.79,9.

A.Fe(OH)3.
B.Fe2(SO4)3.
C.FeO.
D.Fe2O3.