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Tuyển chọn các dạng toán hay lạ khó - Chu Văn Biên (Phần I-IV)

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2 2<br />

2 2 Z Z m 1<br />

L C<br />

1 cos sin <br />

Z m <br />

1<br />

2 1<br />

2 m 1<br />

cos 1 1<br />

3<br />

<br />

<br />

1<br />

2 / 3<br />

1 1 <br />

3 m 1<br />

<br />

m <br />

1<br />

2 / 3<br />

1 f0<br />

50<br />

f0<br />

50 25 6 11, 24Hz<br />

Chọn D.<br />

1<br />

2 / 3 f<br />

Cách 2:<br />

Áp dụng công thức giải nhanh:<br />

0<br />

0<br />

f<br />

50 1<br />

1 f0<br />

11, 24Hz<br />

Chọn D.<br />

f 50 3<br />

Câu 50.<br />

Áp dụng công thức giải nhanh:<br />

0<br />

2<br />

1 cos<br />

f0<br />

<br />

f <br />

f<br />

2<br />

1 cos<br />

f0<br />

<br />

f <br />

60<br />

2<br />

1 0,68 f0<br />

21,83Hz<br />

Chọn A.<br />

f 60<br />

Câu 51.<br />

*Từ<br />

f<br />

f<br />

1<br />

UL<br />

U<br />

0<br />

m f<br />

UC<br />

U f<br />

0<br />

<br />

f<br />

*Khi U<br />

C<br />

<br />

<strong>Chu</strong>Ènď ho¸ ZC<br />

Z m R 2m<br />

1<br />

U <br />

ZL<br />

1<br />

Z Z f<br />

Z m f<br />

2 L:<br />

C<br />

1<br />

1 cos sin 1 <br />

f2 f0<br />

30 20 Hz<br />

<br />

2 30<br />

R<br />

2.2,5 1 2<br />

1 0,8 f0<br />

50Hz<br />

<br />

f0<br />

m 2,5 ZL<br />

1 0,5R<br />

<br />

<br />

ZC<br />

2,5 1, 25R<br />

<br />

Z '<br />

C<br />

2ZC<br />

2,5R<br />

<br />

*Khi f 3 = 10 Hz = f 2 /2 thì ZL<br />

Z<br />

'<br />

L<br />

0, 25R<br />

2<br />

0

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