vâng, áp dụng cho cả nhịp 3/8

nốt đen : 2 phách

nốt trắng : 4 phách

nốt móc đơn : 1 phách 

nốt móc ghép : 0,5 phách 

nốt lặng đơn : 0,5 phách

nốt lặng đen : 1 phách 

nốt đen : 2 phách

nốt trắng : 4 phách

nốt móc đơn : 1 phách 

nốt móc ghép : 0,5 phách 

nốt lặng đơn : 0,5 phách

nốt lặng đen : 1 phách 

Bài tập đọc nhạc số 7 là bài nào

9.

\(\Delta=\left(m-2\right)^2+32>0;\forall m\Rightarrow\) pt luôn có 2 nghiệm pb với mọi m

Theo hệ thức Viet: \(\left\{{}\begin{matrix}x_1+x_2=m-2\\x_1x_2=-8\end{matrix}\right.\)

\(Q=\left(x_1^2-1\right)\left(x_2^2-1\right)=\left(x_1x_2\right)^2-\left(x_1^2+x_2^2\right)+1\)

\(=\left(x_1x_2\right)^2-\left(x_1+x_2\right)^2+2x_1x_2+1\)

\(=\left(-8\right)^2-\left(m-2\right)^2+2.\left(-8\right)+1\)

\(=49-\left(m-2\right)^2\)

Do \(\left(m-2\right)^2\ge0;\forall m\)

\(\Rightarrow49-\left(m-2\right)^2\le49\)

Dấu "=" xảy ra khi \(m-2=0\Rightarrow m=2\)

10.

\(\Delta=m^2-4\left(m-2\right)=\left(m-2\right)^2+4>0;\forall m\)

\(\Rightarrow\) Pt luôn có 2 nghiệm với mọi m

Theo hệ thức VietL \(\left\{{}\begin{matrix}x_1+x_2=m\\x_1x_2=m-2\end{matrix}\right.\)

kết hợp điều kiện đề bài và hệ thức Viet ta được:

\(\left\{{}\begin{matrix}x_1+x_2=m\\x_1-x_2=2\sqrt{5}\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}2x_1=m+2\sqrt{5}\\x_2=x_1-2\sqrt{5}\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x_1=\dfrac{m+2\sqrt{5}}{2}\\x_2=\dfrac{m-2\sqrt{5}}{2}\end{matrix}\right.\)

Thế vào \(x_1x_2=m-2\)

\(\Rightarrow\left(\dfrac{m+2\sqrt{5}}{2}\right)\left(\dfrac{m-2\sqrt{5}}{2}\right)=m-2\)

\(\Leftrightarrow m^2-20=4m-8\)

\(\Leftrightarrow m^2-4m-12=0\Rightarrow\left[{}\begin{matrix}m=6\\m=-2\end{matrix}\right.\)

-Tham khảo c9-10

CTPT: C_nH_2n

PTHH: C_nH_2n + HCl --> C_nH_2n+1Cl

=> \(\%Cl=\dfrac{35,5}{14n+36,5}.100\%=45,223\%\)

=> n = 3

=> CTPT: C₃H₆

=> B

B

My mother used to work at a restaurant 3 years ago but now she doesn't

He used to be the president of Student Union but now he isn't

There used to be many trees - lined in my hometown but now there is none of them

My husband didn't use to do homework but now he does

Children didn't use to play with high-tech devices at an early age

1. My mom used to work at a restaurant

2. He used to be the president of Student Union

3. There used to be many tree-lined street in my hometown.

4. My husband didn't use to do the housework.

5. The children didn't use to play with high-tech devices.

My mother used to work at  restaurant three years ago.

 He used to be the president of Student Union.

There used to be many tree-lined streets in my hometown.

My husband didn't use to do  housework.

childrent didn't use to play with high-tech devices at an early age.  

Bạn phải cho x-y mới tìm đc

\(x+y=3\Rightarrow\left(x+y\right)^2=9\Rightarrow x^2+y^2+2xy=9\)

\(\Rightarrow5+2xy=9\Rightarrow xy=2\)

\(\Rightarrow\left(x-y\right)^2=x^2+y^2-2xy=5-2.2=1\)

\(\Rightarrow x-y=\pm1\)

\(A=\left(x-y\right)\left(x^2+y^2+xy\right)=\pm1.\left(5+2\right)=\pm7\)

B

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