A.hiện tượng cộng hưởng.
B.tự cảm.
C.cảm ứng điện từ.
D.sử dụng từ trường quay.

A.
B.
C.
D.

A.
B.
C.
D.

A.
B.
C.
D.

A.\(7\)
B.\(2\)
C.\(3\)
D.\(8\)

A.\(x \in \left\{ {-1;\,2;\,4} \right\}\).
B.\(x \in \left\{ {1;\,2;\,-4} \right\}\).
C.\(x \in \left\{ {1;\,-2;\,4} \right\}\).
D.\(x \in \left\{ {1;\,2;\,4} \right\}\).

A.\(x =  2\).
B.\(x =  -2\).
C.\(x =  - 4\).
D.\(x =  4\).

A.\(x \in \left\{ { 0;\,\,1} \right\}\).
B.\(x \in \left\{ { - 1;\,\,1} \right\}\).
C.\(x \in \left\{ { - 1;\,\,0} \right\}\).
D.\(x \in \left\{ { 0} \right\}\).

A.\(x \in \left\{ {\sqrt {\frac{5}{4}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{4}}  - \frac{1}{4}} \right\}\).
B.\(x \in \left\{ {\sqrt {\frac{5}{4}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{4}}  + \frac{1}{4}} \right\}\).
C.\(x \in \left\{ {\sqrt {\frac{5}{2}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{2}}  - \frac{1}{4}} \right\}\).
D.\(x \in \left\{ {-\sqrt {\frac{5}{4}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{4}}  +\frac{1}{4}} \right\}\).

A.\(x \in \left\{ {\sqrt {\frac{5}{4}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{4}}  - \frac{1}{4}} \right\}\).
B.\(x \in \left\{ {\sqrt {\frac{5}{4}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{4}}  + \frac{1}{4}} \right\}\).
C.\(x \in \left\{ {\sqrt {\frac{5}{2}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{2}}  - \frac{1}{4}} \right\}\).
D.\(x \in \left\{ {-\sqrt {\frac{5}{4}}  - \frac{1}{4};\,\, - \sqrt {\frac{5}{4}}  +\frac{1}{4}} \right\}\).