\(\overrightarrow{u}=4\overrightarrow{MA}-3\left(\overrightarrow{MA}+\overrightarrow{AB}\right)+\overrightarrow{MA}+\overrightarrow{AC}-2\left(\overrightarrow{MA}+\overrightarrow{AD}\right)\)

\(=-3\overrightarrow{AB}+\overrightarrow{AC}-2\overrightarrow{AD}=-3\left(\overrightarrow{AB}+\overrightarrow{AD}\right)+\overrightarrow{AC}+\overrightarrow{AD}\)

\(=-3\overrightarrow{AC}+\overrightarrow{AC}+\overrightarrow{AD}=-2\overrightarrow{AC}+\overrightarrow{AD}\)

\(\overrightarrow{u}^2=\left(-2\overrightarrow{AC}+\overrightarrow{AD}\right)^2=4AC^2-4\overrightarrow{AC}.\overrightarrow{AD}+AD^2\)

\(=4\left(a\sqrt{2}\right)^2-4.a\sqrt{2}.a.cos45^0+a^2=5a^2\)

\(\Rightarrow\left|\overrightarrow{u}\right|=a\sqrt{5}\)

41. A 42. B 43.C 44.A 45.D

Câu 44: C

Câu 45: C

41. Roger: " I don't believe it. " - Anita: " ..................... "

→ Đáp án:                C. Neither do I   

42. Jill : " Do you know Lisa's an excellent pianist ? - Maria: " ..................... "

→ Đáp án:                B. Yes, she does 

43. Karen: " ............... this word in English ? " - Betsy: " C-O-Z-Y "

→ Đáp án:                B. How do you spell    

44. Customer: " I think my change is wrong. " - Shop assistant: " ................... "

→ Đáp án:                C. Sorry. I don't think I have any change  

45. Mandy: " I've got a toothache. " - George: " ................. " 

→ Đáp án:                D. Why don't you see the dentist ? 

Ta có: \(L=4\pi10^{-7}\dfrac{N^2}{l}S=4\pi10^{-7}\dfrac{1000^2}{\dfrac{50}{100}}\left(\pi\cdot\left(\dfrac{10}{100}\right)^2\right)\approx0,1\left(H\right)\)

Độ lớn suất điện động tự cảm:

\(e_{tc}=L\dfrac{\Delta i}{\Delta t}=0,1\dfrac{10-2}{0,01}\approx63,2V\)

Chọn D

a c d a d

Câu 42:

Δ1: VTPT là (m;-1)

Δ2: VTPT là (2;-1)

Để Δ1 vuông góc Δ2 thì m*2+(-1)*(-1)=0

=>2m+1=0

=>m=-1/2