Question

Tính giá trị biểu thức trên

1/10+1/15+1/21+...+1/4950

Answer 1

Đặt A= \(\dfrac{1}{10}+\dfrac{1}{15}+\dfrac{1}{21}+......+\dfrac{1}{4950}\)

A.\(\dfrac{1}{2}=\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+......+\dfrac{1}{9900}\)

A.\(\dfrac{1}{2}=\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+......+\dfrac{1}{99.100}\)

A.\(\dfrac{1}{2}=\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+.......+\dfrac{1}{99}\)\(-\dfrac{1}{100}\)

A.\(\dfrac{1}{2}=\dfrac{1}{4}-\dfrac{1}{100}\)

A.\(\dfrac{1}{2}=\dfrac{6}{25}\)

A=\(\dfrac{6}{25}:\dfrac{1}{2}\)

A=\(\dfrac{12}{25}\)

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