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hello nha

mình lớp 12 nha

Em viết phần intro nha:

The chart above decsribes how the birth rates of 2 countries namely China, USA changed in 80 years which started from 1920

Answer:
The line graph compares the birth rates in China and the US and how these rates changed from 1920 to 2000.
Overall, there was a general decline in fertility of both nations throughout the time surveyed. However, the US’s birth rates almost was higher than that of China over the whole period.
American saw a significant fluctuation in the birth rates between 1920 to 1935, but it always remained over 10%. However, in the following decade, the fertility of the US decreased sharply to under 5 %. From 1945 to 1950, there was a rapidly increased in American’s birth rates, at 15%, reaching the highest point of it’s own during the whole period. From that on, the fertility of the US fell gradually to 7% in 2000.
During the 80-year period, the birth rates in China changed more significantly than in the US. It fell down to 5% in the year 1940, then reaching a peak of whole line graph in 1950, at 20%. Over the remainder of the period, China saw a sharply drop in the birth rates to only about 2% until 2000.

bằng 2 

k nha

a2 b3 c4 d5

tương lai

ngày mai!bn lên gg mà tra!

Câu 49: 

Khối chóp tam giác đều \(S.ABC\)chiều cao \(SO\).

\(S_{ABC}=\frac{\left(2a\sqrt{3}\right)^2\sqrt{3}}{4}=3\sqrt{3}a^2\)

\(SO=\frac{3V_{S.ABC}}{S_{ABC}}=\frac{6a^3}{3\sqrt{3}a^2}=\frac{2\sqrt{3}}{3}\)

Chọn C. 

Câu 48: 

Chóp tam giác đều \(S.ABC\), \(G\)là trọng tâm tam giác \(ABC\).

\(AG=\frac{AB\sqrt{3}}{3}=\frac{a\sqrt{3}}{3}\)

\(SG=tan60^o.AG=a\)

\(V_{S.ABC}=\frac{1}{3}.SG.S_{ABC}=\frac{1}{3}.a.\frac{a^2\sqrt{3}}{4}=\frac{a^3\sqrt{3}}{12}\)

Chọn C.

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Có 3 bước này nek !! Bn tham khảo nhá !! Chúc BN ~HT~

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