a) Tính tổng: S = (-1/7)0 + (-1/7)1 + (-1/7)2 +...+ (-1/7)2007
b) Thực hiện phép tính: M = 1 + 1/2*(1+2) + 1/3*(1+2+3) + 1/4*(1+2+3+4) +...+ 1/16*(1+2+3+...+16)
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25 tháng 3 2021
a) Xét Tam giác ABC và Tam giác ECM
có: BM = CM (M là trung điểm của BC)
AMB = EMC ( Đối đỉnh)
AM = EM (M là trung điểm của AE)
=> Tam giác ABC = Tam giác ECM (c. g .c) (đpcm)
b) Vì AB < AC
mà AB = EC
=> EC < AC
=>EAC < AEC (quan hệ giữa góc và cạnh đối diện )
=>MAC < MEC
Mà MAB = MEC (Tam giác ABC = Tam giác ECM)
=>MAC < MAB
25 tháng 3 2021
a/ Xét ΔABM và ΔECM có:
MB=MC (Mlà trung điểm của BC)
góc AMB = góc EMC ( 2 góc đối đỉnh)
MA=ME(giả thiết)
Do đó ΔABM=ΔECM(c.g.c)
b/ MAC<MAB
25 tháng 3 2021
bạn ế thật rồi,năm nay là năm 2021 mà bạn vẫn chưa có ai trả lời
25 tháng 3 2021
hình 2
_ I see a man is holding a child and a woman is going to work.
_I can see that in the future, men will take care of children, cook rice, ... and women will be the backbone of the family to make money to feed everyone in the house. But today, in complete contrast, men are the breadwinner of the family, and women stay home to take care of their babies, and cook housework.
_I think this transition is not very appropriate for men, which are healthier than women, so they will do heavy work. Women are weaker than men, so they will do light work such as taking care of children , cooking rice , doing housework
25 tháng 3 2021
2. The problems faced by the company, which I'll look at in detail in a moment, are being resolved.
3. She was greatly influenced by her father, who/ whom she adored.
4. Parents whose children are between four and six are being asked to take part in the survey.
5. He isn't looking forward to the time when he will have to leave.
6. The Roman coins, which a local farmer came across in a field, are now on display in the National Museum.
7. He pointed to the stairs which/that led down to the cellar.
8. These drugs, which are used to treat stomach ulcers, have been withdrawn from sale.
9. The singer, who was recovering from flu, had to cancel her concert.
10. We went to the Riverside Restaurant where I once had lunch with Henry.
11. My aunt, whose first job was filling shelves in a supermarket, is now a manager of a department store.
12. John Graham‟s latest film, which is set in the north of Australia, is his first for more than five years.
13. The newspaper is owned by the Mears group, whose chairperson is Sir James Hex.
14. The Master's course, which I took in 1990, is no longer taught.
15. The minister talked about the plans for tax reform (that/which) he will reveal next month.
25 tháng 3 2021
2. The problems faced by the company, which I'll look at in detail in a moment, are being resolved.
3. She was greatly influenced by her father, who/ whom she adored.
4. Parents whose children are between four and six are being asked to take part in the survey.
5. He isn't looking forward to the time when he will have to leave.
6. The Roman coins, which a local farmer came across in a field, are now on display in the National Museum.
7. He pointed to the stairs which/that led down to the cellar.
8. These drugs, which are used to treat stomach ulcers, have been withdrawn from sale.
9. The singer, who was recovering from flu, had to cancel her concert.
10. We went to the Riverside Restaurant where I once had lunch with Henry.
11. My aunt, whose first job was filling shelves in a supermarket, is now a manager of a department store.
12. John Graham‟s latest film, which is set in the north of Australia, is his first for more than five years.
13. The newspaper is owned by the Mears group, whose chairperson is Sir James Hex.
14. The Master's course, which I took in 1990, is no longer taught.
15. The minister talked about the plans for tax reform that he will reveal next month.
a) \(S=\left(-\frac{1}{7}\right)^0+\left(-\frac{1}{7}\right)^1+\left(-\frac{1}{7}\right)^2+...+\left(-\frac{1}{7}\right)^{2007}\)
\(=1+\left(-\frac{1}{7}\right)+\left(-\frac{1}{7}\right)^2+...+\left(-\frac{1}{7}\right)^{2007}\)
=> 7S = \(7+\left(-1\right)+\left(-\frac{1}{7}\right)+...+\left(-\frac{1}{7}\right)^{2006}\)
Lấy 7S trừ S ta có :
7S - S = \(7+\left(-1\right)+\left(-\frac{1}{7}\right)+...+\left(-\frac{1}{7}\right)^{2006}-\left[1+\left(-\frac{1}{7}\right)+\left(-\frac{1}{7}\right)^2+...+\left(-\frac{1}{7}\right)^{2007}\right]\)
6S = \(7-1-1+\left(\frac{1}{7}\right)^{2007}=5+\left(\frac{1}{7}\right)^{2007}\Rightarrow S=\frac{5+\left(\frac{1}{7}\right)^{2007}}{6}\)