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

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Đặt Z xR . 2<br />

L<br />

R2L<br />

2 1 2<br />

Xét tan <br />

<br />

R2L<br />

ZL<br />

ZL<br />

<br />

x<br />

x <br />

tan<br />

tan<br />

R R R 3 2 1<br />

<br />

1<br />

tan<br />

3<br />

R2L<br />

tan<br />

ZL<br />

ZL<br />

x<br />

1 . 1 x.<br />

x 3<br />

R R R 3 x<br />

2 1 2<br />

2 3<br />

1<br />

<br />

tan R2L<br />

2 <br />

max<br />

R L<br />

<br />

<br />

max<br />

3<br />

6<br />

Câu 36.<br />

Khi L t<strong>hay</strong> đổi thì<br />

Chọn A.<br />

U<br />

R max<br />

và<br />

UCmax<br />

<br />

cộng hưởng<br />

U<br />

R max<br />

U<br />

U <br />

Imax<br />

<br />

U<br />

R U I Z Z<br />

<br />

R<br />

C max max C C<br />

U<br />

Lmax<br />

U R Z<br />

<br />

R<br />

2 2<br />

C<br />

Theo bài ra: U<br />

Lmax<br />

3U<br />

R max<br />

<strong>hay</strong><br />

U R Z<br />

2 2<br />

C<br />

R<br />

3U Z 2 2R<br />

C<br />

2 2 2 2<br />

U R Z<br />

Lmax<br />

C R R .8 5<br />

<br />

U Z 2 2R<br />

2<br />

C max<br />

Câu 37.<br />

Cách 1:<br />

C<br />

Chọn B.<br />

Áp dụng định lý hàm số sin cho tam giác ANB:<br />

U<br />

U<br />

RL<br />

UC<br />

<br />

<br />

RL<br />

<br />

sin RL<br />

sin <br />

2 2 <br />

sin

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