Question

 

cần gấp hứa tick

Answer 1

\(=\dfrac{2}{3}\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+...+\dfrac{3}{97\cdot100}\right)\)

\(=\dfrac{2}{3}\left(1-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{100}\right)\)

\(=\dfrac{2}{3}\cdot\dfrac{99}{100}=\dfrac{66}{100}=\dfrac{33}{50}\)

Answer 2

`2/(1.4) + 2/(4.7) + ...+ 2/(97.100)`

`=2*(1/(1.4) + 1/(4.7) + ...+ 1/(97.100) )`

`=2*(1 -1/4 +1/4 -1/7 + ...+1/97 -1/100)`

`=2*(1-1/100) `

`=2*( 100/100 -1/100)`

`=2* 99/100`

`=198/100 = 99/50`