A.
\(\left\{ \begin{array}{l}
a < 0\\
\Delta \le 0
\end{array} \right.\)
B.
\(\left\{ \begin{array}{l}
a \le 0\\
\Delta < 0
\end{array} \right.\)
C.
\(\left\{ \begin{array}{l}
a < 0\\
\Delta \ge 0
\end{array} \right.\)
D.
\(\left\{ \begin{array}{l}
a > 0\\
\Delta \le 0
\end{array} \right.\)
A. \({x^2} + 2{y^2} - 4x - 8y + 1 = 0.\)
B. \({x^2} + {y^2} - 4x + 6y - 12 = 0.\)
C. \({x^2} + {y^2} - 2x - 8y + 20 = 0.\)
D. \(4{x^2} + {y^2} - 10x - 6y - 2 = 0.\)
A. \(\frac{{{x^2}}}{2} + \frac{{{y^2}}}{3} = 1\)
B. \(\frac{{{x^2}}}{9} - \frac{{{y^2}}}{8} = 1\)
C. \(\frac{x}{9} + \frac{y}{8} = 1\)
D. \(\frac{{{x^2}}}{9} + \frac{{{y^2}}}{1} = 1\)
A. \(x = - 3\)
B. \(x = \frac{5}{2}\)
C. \(x=4\)
D. \(x=2\)
A. \(M\left( {\frac{7}{2};0} \right)\) và \(M\left( {1;0} \right)\)
B. \(M\left( {\sqrt {13} ;0} \right)\)
C. \(M\left( {4;0} \right)\)
D. \(M\left( {2;0} \right)\)
A. \(I\left( { - 2; - 3} \right).\)
B. \(I\left( { 2; 3} \right).\)
C. \(I\left( {4;6} \right).\)
D. \(I\left( {-4;-6} \right).\)
A. \({x^2} + {y^2} + 25x + 19y - 49 = 0.\)
B. \(2{x^2} + {y^2} - 6x + y - 3 = 0.\)
C. \({x^2} + {y^2} - 6x + y - 1 = 0.\)
D. \({x^2} + {y^2} - 6x + xy - 1 = 0.\)
A. \(\tan \left( {\alpha + \beta } \right) = 2\cot \alpha \)
B. \(\tan \left( {\alpha + \beta } \right) = 2\cot \beta \)
C. \(\tan \left( {\alpha + \beta } \right) = 2\tan \beta \)
D. \(\tan \left( {\alpha + \beta } \right) = 2\tan \alpha \)
A. \(A = \cot 6x.\)
B. \(A = \cot 3x.\)
C. \(A = \cot 2x.\)
D. \(A = \tan x + \tan 2x + \tan 3x.\)
A. \(\cos 2a = {\cos ^2}a--{\sin ^2}a.\)
B. \(\cos 2a = {\cos ^2}a + {\sin ^2}a.\)
C. \(\cos 2a = 2{\cos ^2}a + 1.\)
D. \(\cos 2a = 2{\sin ^2}a - 1.\)
A. \(x + 2y + 1 = 0.\)
B. \(2x - y = 0.\)
C. \( - x + 2y + 1 = 0.\)
D. \( - 2x + 4y - 1 = 0.\)
A. \(\cos \left( {a + \frac{\pi }{3}} \right) = \cos a + \frac{1}{2}\)
B. \({\rm{cos}}\left( {a + \frac{\pi }{3}} \right) = \frac{1}{2}\sin a - \frac{{\sqrt 3 }}{2}\cos a\)
C. \({\rm{cos}}\left( {a + \frac{\pi }{3}} \right) = \frac{{\sqrt 3 }}{2}\sin a\, - \frac{1}{2}\cos a\)
D. \({\rm{cos}}\left( {a + \frac{\pi }{3}} \right) = \frac{1}{2}{\rm{cos}}a - \frac{{\sqrt 3 }}{2}\sin a\)
A. \(A=0\)
B. \(A = - 2\cot x\)
C. \(A = \sin 2x\)
D. \(A = - 2\sin x\)
A. \({a^2} = {b^2} + {c^2} + 2bc\cos A\)
B. \({a^2} = {b^2} + {c^2} - 2bc\cos A\)
C. \({a^2} = {b^2} + {c^2} - 2bc\cos C\)
D. \({a^2} = {b^2} + {c^2} - 2bc\cos B\)
A. \(\{ 1\} \cup [4; + \infty )\)
B. \(( - \infty ;1] \cup [3; + \infty )\)
C. \(( - \infty ;1] \cup [4; + \infty )\)
D. \([4; + \infty )\)
A. \(\frac{{{\rm{7}}\sqrt 2 }}{2}.\)
B. 8
C. \({\rm{8}}\sqrt 3 \,.\)
D. \({\rm{80}}\sqrt 3 \,.\)
A. \(\frac{{\sqrt {21} }}{3}\)
B. \(-\frac{{\sqrt {21} }}{5}\)
C. \(\frac{{\sqrt {21} }}{5}\)
D. \(-\frac{{\sqrt {21} }}{2}\)
A. \(\cos a\cos b = \frac{1}{2}\left[ {\cos \left( {a--b} \right) + \cos \left( {a + b} \right)} \right].\)
B. \(\sin a\cos b = \frac{1}{2}\left[ {\sin \left( {a - b} \right) - \cos \left( {a + b} \right)} \right].\)
C. \(\sin a\sin b = \frac{1}{2}\left[ {\cos \left( {a--b} \right)--\cos \left( {a + b} \right)} \right].\)
D. \(\sin a\cos b = \frac{1}{2}\left[ {\sin \left( {a--b} \right) + \sin \left( {a + b} \right)} \right].\)
A. \(\overrightarrow n = ( - 2; - 1)\)
B. \(\overrightarrow n = (2; - 1)\)
C. \(\overrightarrow n = ( - 1;2)\)
D. \(\overrightarrow n = \left( {1;2} \right)\)
A. \(\left( { - \frac{1}{2};2} \right)\)
B. \(\left[ {\frac{1}{2};2} \right)\)
C. \(\left( { - 2;\frac{1}{2}} \right]\)
D. \(\left[ { - 2;\frac{1}{2}} \right)\)
A. \(f(x) < 0\) với mọi \(x \in R\)
B. \(f(x) \ge 0\) với mọi \(x \in R\)
C. \(f(x) \le 0\) với mọi \(x \in R\)
D. \(f(x) > 0\) với mọi \(x \in R\)
A. 21
B. 23
C. 22
D. 20
A. \(S = \left( {0; + \infty } \right)\)
B. \(S = \left( { - \infty ;0} \right)\)
C. \(S = \left( { - 4;2} \right)\)
D. \(S = (2; + \infty )\)
A. \(\overrightarrow {{n_1}} = \left( {3;2} \right)\)
B. \(\overrightarrow {{n_2}} = \left( { - 4; - 6} \right)\)
C. \(\overrightarrow {{n_3}} = \left( {2; - 3} \right)\)
D. \(\overrightarrow {{n_4}} = \left( { - 2;3} \right)\)
A. \(\cos \left( {a--b} \right) = \cos a.sinb + \sin a.\sin b.\)
B. \(\sin \left( {a--b} \right) = \sin a.\cos b - \cos a.\sin b.\)
C. \(\sin \left( {a + b} \right) = \sin a.\cos b - {\mathop{\rm cosa}\nolimits} .\sin b.\)
D. \(\cos \left( {a + b} \right) = \cos a.\cos b + \sin a.\sin b.\)
A. \(\frac{{\sqrt {10} }}{{10}}.\)
B. \(\frac{3}{{10}}\)
C. \(\frac{3}{5}.\)
D. \(\frac{{3\sqrt {10} }}{{10}}.\)
A. \(m \in \emptyset \)
B. \(m \in \left( { - 2;2} \right)\)
C. \(m \in \left( { - \infty ; - 2} \right] \cup \left[ {2; + \infty } \right)\)
D. \(m \in \left[ { - 2;2} \right]\)
A. \(\frac{{{x^2}}}{{25}} + \frac{{{y^2}}}{4} = 1.\)
B. \(\frac{{{x^2}}}{{29}} + \frac{{{y^2}}}{{25}} = 1.\)
C. \(\frac{{{x^2}}}{{25}} + \frac{{{y^2}}}{{21}} = 1.\)
D. \(\frac{{{x^2}}}{{25}} + \frac{{{y^2}}}{{29}} = 1.\)
A. \(f\left( x \right) > 0\) với \(\forall x \in \left( { - \infty ;\frac{{20}}{{23}}} \right)\)
B. \(f\left( x \right) > 0\) với \(\forall x > - \frac{5}{2}\)
C. \(f\left( x \right) > 0\) với \(\forall x \in R\)
D. \(f\left( x \right) > 0\) với \(\forall x \in \left( {\frac{{20}}{{23}}; + \infty } \right)\)
A. \(2x - y - 3 = 0\)
B. \(x - 2y = 0\)
C. \(x + 2y - 4 = 0\)
D. \(x - y - 1 = 0\)
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