A = \(\dfrac{2}{2.3}\) + \(\dfrac{2}{3.4}\) + \(\dfrac{2}{4.5}\) + ... + \(\dfrac{2}{199.200}\)

A = 2. (\(\dfrac{1}{2.3}\) + \(\dfrac{1}{3.4}\) + \(\dfrac{1}{4.5}\) + ... + \(\dfrac{1}{199.200}\))

A = 2.(\(\dfrac{1}{2}\) - \(\dfrac{1}{3}\) + \(\dfrac{1}{3}\) - \(\dfrac{1}{4}\) + \(\dfrac{1}{4}\) - \(\dfrac{1}{5}\) + ... + \(\dfrac{1}{199}\) - \(\dfrac{1}{200}\))

A = 2.(\(\dfrac{1}{2}\) - \(\dfrac{1}{200}\))

A = 2. \(\dfrac{99}{200}\)

A = \(\dfrac{99}{100}\)

Lời giải:
Gọi tổng trên là $A$

$A=2(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{199.200})$

$=2(\frac{3-2}{2.3}+\frac{4-3}{3.4}+\frac{5-4}{4.5}+...+\frac{200-199}{199.200})$

$=2(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{199}-\frac{1}{200})$

$=2(\frac{1}{2}-\frac{1}{200})=1-\frac{1}{100}=\frac{99}{100}$

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Nóiiiiiiiiiiiii nhanhhhhhh

Ngăn cản Lan ko viết vào truyện vì truyện này ko phải của Lan

How many hours do you spend watching television?

Giúp mk nhanh câu này với ạ!

Bạn muốn hỏi gì?

là sao ạ?

bước đó là thương không quá 10 ok chứ

là bước gì ạ?

1.Susan has a headache and a bad fever. She also has a stomachache and a sore throat.

2.She should not fruits because she has a stomachache.

3.Susan shouldn't eat ice cream. Ice cream is not good for her throat now.

4.The doctor said that Susan should take a rest for a week.

ko bt đúng hay sai nhưng cho mình 1 like nhé

1. She has a headache, a bad fever, sore throat and stomachache

2. She should not eat to much fruit.
3. Susan should not eat ice cream because it not good for her throat now.
4. She should stay home for a week

1.Nam has a toothache.He should go to dentist

2.Hoa has a sore throat.She should not talk too much and drink cold water

3. Hung has a headache.He should take a rest and some medicine

4. Phong has a backache.He should not carry heavy things

5.Huong has a stomachache.She should go to the doctor

2. Hoa has a sore throat. She should not talk too much and drink cold water. 

3. Hung has a headache. He should take a rest and some medicine. 

4. Phong has a backache. He should not carry heavy things. 

5. Huong has a stomachache. She should go to the doctor.