Question

giúp mình vợi ạ

Answer 1

bài 6 :
\(\dfrac{1}{5}+\dfrac{-1}{6}+\dfrac{1}{7}+\dfrac{-1}{8}+\dfrac{1}{9}+\dfrac{1}{8}+\dfrac{-1}{7}+\dfrac{1}{6}+\dfrac{-1}{5}\)

= \(\dfrac{1}{5}+\dfrac{-1}{6}+\dfrac{1}{7}+\dfrac{-1}{8}+\dfrac{1}{9}+\dfrac{1}{8}+\dfrac{-1}{7}+\dfrac{1}{6}+\dfrac{-1}{5}\)

= \(\left(\dfrac{1}{5}+\dfrac{-1}{5}\right)+\left(\dfrac{-1}{6}+\dfrac{1}{6}\right)+\left(\dfrac{1}{7}+\dfrac{-1}{7}\right)+\left(\dfrac{1}{8}+\dfrac{-1}{8}\right)+\dfrac{1}{9}\)

= \(0+0+0+0+\dfrac{1}{9}\)

= \(\dfrac{1}{9}\)

bài 7 : 
a) 1/2 ; 1/6 ; 1/12 ; 1/20 ; 1/30 ; 1/42

sai mog bạn thông cảm ^^