a, \(I_1=I_3=2I_2\)

\(I_2=\dfrac{7,8}{12}=0,65\left(A\right)\) \(\Rightarrow I_3=I_1=1,3\left(A\right)\)

\(\Rightarrow U_3=7,8-U_1=7,8-1,3.4=2,6\left(V\right)\)

\(\Rightarrow R_3=\dfrac{2,6}{1,3}=2\left(\Omega\right)\)

b, k đóng ta có mạch (R1//R2)nt(R3//R4)

\(\Rightarrow R_{tđ}=\dfrac{4.6}{10}+\dfrac{2.6}{8}=3,9\left(\Omega\right)\)

\(\Rightarrow I_k=\dfrac{7,8}{3,9}=2\left(A\right)\)

\(\Rightarrow U_{12}=\dfrac{4.6}{10}=2,4\left(V\right)\)

\(\Rightarrow U_{34}=2.1,5=3\left(V\right)\)

\(\Rightarrow I_1=\dfrac{2,4}{4}=0,6\left(A\right);I_2=\dfrac{2,4}{6}=0,4\left(A\right)\)

\(\Rightarrow I_3=\dfrac{3}{2}=1,5\left(A\right);I_4=\dfrac{3}{6}=0,5\left(A\right)\)

Câu 3:

2: Xét tứ giác OKEH có 

\(\widehat{OKE}=\widehat{OHE}=\widehat{KOH}=90^0\)

Do đó: OKEH là hình chữ nhật

mà đường chéo OE là tia phân giác của \(\widehat{KOH}\)

nên OKEH là hình vuông

Bạn tách bớt ra nhé!

giúp j?????

51 Because it rained heavily, we were late for school

52 We used to be made to clean the house by my mother

53 She said she was working in a restaurant, and didn't care much for it

54 I haven't spoken to her for 2 years

55 It is interesting to go swimming in the river in the summer

46 They wish they didn't have to work in a noisy office

47 They used to make a lỏ of mistake in spelling

48 It's high time you went to bed

49 Neither my sister nor I am good at swimming

50 If he works hard, he will pass the exam

51 The last time I was to a concert was over a year ago

52 I wish I were able to fly a plane

53 I'm bored with this film

54 My question hasn't been answered properly

55 If she were on booard now, she could experienced these maverlous things

\(A=2^{2022}-2^{2020}+...+2^2-1\)

\(\Rightarrow4A=2^{2024}-2^{2022}+...+2^4-2^2\)

\(\Rightarrow A+4A=2^{2024}-1\)

\(\Rightarrow5A=2^{2024}-1\)

Đồng thời: \(B=2^{2023}\Rightarrow2B=2^{2024}\)

Mà \(2^{2024}>2^{2024}-1\)

\(\Rightarrow5A< 2B\)

Lời giải:
a. Số hs lớp 6D là: $2+4+7+15+10+6+4=48$ (hs) 

b. Số hs điểm giỏi là: $6+4=10$ (hs) 

Số hs điểm giỏi chiếm số phần trăm là: $10:48.100=20,83$ (%)

a, khi K mở \(=>[\left(R1ntR2\right)//\left(R3ntR4\right)]ntR5\)

ampe kế chỉ 0,5A\(=>I\left(A\right)=Im=I5=I1234=0,5A\)

\(=>U5=I5.R5=0,5.15=7,5V\)

\(=>U1234=Um-U5=12-7,5=4,5V\)

\(=>R1234=\dfrac{U1234}{I1234}=\dfrac{\left(R1+R2\right)\left(R3+R4\right)}{R1+R2+R3+R4}\)

\(< =>\dfrac{4,5}{0,5}=\dfrac{\left(12+R2\right)\left(4+8\right)}{24+R2}=9=>R2=24\left(om\right)\)

b, ta có R2=24 

\(\Rightarrow\dfrac{R_1}{R_3}=\dfrac{R_2}{R_4}\) mạch cầu cb

cđ dđ qua K bằng 0

\(R_{tđ}=\dfrac{R_{12}.R_{34}}{R_{12}+R_{34}}+R_5+R_a=25\left(\Omega\right)\)

\(\Rightarrow I_a=\dfrac{12}{25}=0,48\left(A\right)\)