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

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

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

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

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:

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:

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

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

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

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

:v bạn tách nhỏ đề ra và chụp ngang ra nhé

(3x)^2=3^2.x^2=9x^2

1: \(\overrightarrow{AG}=\dfrac{1}{3}\overrightarrow{AB}+\dfrac{1}{3}\overrightarrow{AC}\)