Bài 4:

7 dm³ sắt cân nặng số kg là:

$109,2.\frac{7}{14}=54,6$ (kg)

Bài 3:

a. Đặt $y=kx$. Ta có:
$y_1=kx_1$

$y_2=kx_2$

$\Rightarrow y_1+y_2=k(x_1+x_2)$

$\Leftrightarrow 15=k(-3)\Rightarrow k=-5$

Vậy $y=-5x$

Với $y=2$ thì $x=\frac{y}{-5}=\frac{-2}{5}$

Với $y=9$ thì $x=\frac{9}{-5}$

1 There are 5000 living languages in the world

2 It is Chinese

3 It is English

4 Yes, because I think English is interesting

V

1 He used to play the guitar at night

2 She wishes she had a pen pal

3 We started learning E 4 years ago

4 How long have you had that car

Bài 3: 

Xét ΔIAB có 

\(\widehat{AIB}+\widehat{IAB}+\widehat{IBA}=180^0\)

\(\Leftrightarrow\widehat{IAB}+\widehat{IBA}=115^0\)

hay \(\widehat{DAB}+\widehat{ABC}=230^0\)

Xét tứ giác ABCD có 

\(\widehat{D}+\widehat{C}+\widehat{DAB}+\widehat{CBA}=360^0\)

\(\Leftrightarrow\widehat{D}+\widehat{C}=150^0\)

mà \(\widehat{C}-\widehat{D}=10^0\)

nên \(2\cdot\widehat{C}=160^0\)

\(\Leftrightarrow\widehat{C}=80^0\)

\(\Leftrightarrow\widehat{D}=70^0\)

Bài 1: 

a) Ta có: \(A=\left(\dfrac{6+\sqrt{20}}{3+\sqrt{5}}+\dfrac{\sqrt{14}-\sqrt{2}}{\sqrt{7}-1}\right):\left(2+\sqrt{2}\right)\)

\(=\left(2+\sqrt{2}\right)\cdot\dfrac{1}{2+\sqrt{2}}\)

=1

b) Ta có: \(B=\sqrt{5-2\sqrt{6}}+\sqrt{5+2\sqrt{6}}-\dfrac{11}{2\sqrt{3}+1}\)

\(=\sqrt{3}-\sqrt{2}+\sqrt{3}+\sqrt{2}-2\sqrt{3}+1\)

=1

Bài 2: 

b) Ta có: \(\sqrt{9x^2-9}+\sqrt{4x^2-4}=\sqrt{16x^2-16}+2\)

\(\Leftrightarrow3\sqrt{x^2-1}+2\sqrt{x^2-1}-4\sqrt{x^2-1}=2\)

\(\Leftrightarrow x^2-1=4\)

\(\Leftrightarrow x\in\left\{\sqrt{5};-\sqrt{5}\right\}\)

284,91

417,12

a.284,91

b.417,12

Nha^^

1c  2.a  3b  4a

chết cái đáp án dưới là của bài 2 đây là của bài 1

1d   2a  3d  4c  5b

Bài 3:

a. \(R=R1+R2=15+30=45\Omega\)

b. \(\left\{{}\begin{matrix}I=U:R=9:45=0,2A\\I=I1=I2=0,2A\left(R1ntR2\right)\end{matrix}\right.\)

c. \(\left\{{}\begin{matrix}U1=R1.I1=15.0,2=3V\\U2=R2.I2=30.0,2=6V\end{matrix}\right.\)

Bài 4:

\(I1=U1:R1=6:3=2A\)

\(\Rightarrow I=I1=I2=2A\left(R1ntR2\right)\)

\(U=R.I=\left(3+15\right).2=36V\)

\(U2=R2.I2=15.2=30V\)