mmm
K
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LD
7
17 tháng 10 2021
1, Sure. Where do you want to go
2, Oh, the mall's on the Teeth Street
3,Go stright down FA and turn left
4, That's right. The mall is next to the museum
5,You're welcome
KY
17 tháng 10 2021
Drag the correct sentences to complete the conversation.
A: Excuse me. Can you help me?
B: ____________Sure. Where do you want to go?____________________________
A: I want to go to the mall.
B: ___________Oh. The mall's on the Tenth street_____________________________
A: Mmm... where's Tenth Street?
B: ___________Go straight down first..._____________________________
A: So, straight and then left at the corner?
B: _____________That's right....___________________________
A: Got it. Thanks.
B: _____________You're welcome___________________________
Bài toán 14:
a) \(B=1+3+3^2+3^3+...+3^{2006}\)
\(\Rightarrow3B=3\left(1+3+3^2+3^3+...+3^{2006}\right)\)
\(\Rightarrow3B=3+3^2+3^3+...+3^{2007}\)
b) Ta có: \(3B=3+3^2+3^3+3^4+...+2^{2007}\)
\(\Rightarrow3B-B=\left(3+3^2+3^3+...+3^{2007}\right)-\left(1+3+3^2+3^3+...+3^{2006}\right)\)
\(\Rightarrow2B=\left(3-3\right)+\left(3^2-3^2\right)+\left(3^3-3^3\right)+...+\left(3^{2007}-1\right)\)
\(\Rightarrow2B=3^{2007}-1\)
\(\Rightarrow B=\left(3^{2007}-1\right):2\)
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