tính nhanh: 1191919/121212 + 191919/202020 + 191919/303030 + 191919/424242 + 191919/565656

0 bình luận về “tính nhanh: 1191919/121212 + 191919/202020 + 191919/303030 + 191919/424242 + 191919/565656”

1. `191919/121212 + 191919/202020 + 191919/303030 + 191919/424242 + 191919/565656`
   

   `=19/12+19/20+19/30+19/42+19/56`

   `=19(1/12+1/20+1/30+1/42+1/56)`
   

   `=19(1/3.4+1/4.5+1/5.6+1/6.7+1/7.8)`
   

   `=19(1/3-1/4+1/4-1/5+…+1/7-1/8)`
   

   `=19(1/3-1/8)=19(8/24-3/24)=19. 5/24=19/1. 5/24=95/24`

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2. $\ \dfrac{191919}{121212} + \dfrac{191919}{202020} + \dfrac{191919}{303030} + \dfrac{191919}{424242} + \dfrac{191919}{565656}$

   $\ = \dfrac{191919 : 10101}{121212 : 10101} + \dfrac{191919 : 10101}{202020 : 10101} + \dfrac{191919 : 10101}{303030 : 10101} + \dfrac{191919 : 10101}{424242 : 10101} + \dfrac{191919 : 10101}{565656 : 10101}$

   $\ = \dfrac{19}{12} + \dfrac{19}{20} + \dfrac{19}{30} + \dfrac{19}{42} + \dfrac{19}{56}$

   $\ = 19(\dfrac{1}{3.4} + \dfrac{1}{4.5} + \dfrac{1}{5.6} + \dfrac{1}{6.7} + \dfrac{1}{7.8})$

   $\ = 19(\dfrac{1}{3} – \dfrac{1}{4} + \dfrac{1}{4} – \dfrac{1}{5} + \dfrac{1}{5} – \dfrac{1}{6} + \dfrac{1}{6} – \dfrac{1}{7} + \dfrac{1}{7} – \dfrac{1}{8})$

   $\ = 19(\dfrac{1}{3} – \dfrac{1}{8})$

   $\ = 19. \dfrac{8-3}{24} = 19 . \dfrac{5}{24} = 3\dfrac{23}{24}$

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