Tính tổng 1/ 1 + (-2) + 3 + (-4) + . . . + 19 + (-20) 2/ 1 – 2 + 3 – 4 + . . . + 99 – 100 3/ 2 – 4 + 6 – 8 + . . . + 48 – 50 4/ – 1 + 3 – 5 + 7 – .

0 bình luận về “Tính tổng 1/ 1 + (-2) + 3 + (-4) + . . . + 19 + (-20) 2/ 1 – 2 + 3 – 4 + . . . + 99 – 100 3/ 2 – 4 + 6 – 8 + . . . + 48 – 50 4/ – 1 + 3 – 5 + 7 – .”

1. 1/ 1 + (-2) + 3 + (-4) + . . . + 19 + (-20)

   =1-2+3-4+…+19-20

   =(1-2)+(3-4)+…+(19-20)

   =(-1)+(-1)+…+(-1)
   =(-1).10

   =-10

   2/ 1 – 2 + 3 – 4 + . . . + 99 – 100

   =(1-2)+(3-4)+…+(99-100)

   =(-1)+(-1)+…+(-1)

   =(-1).50

   =-50

   3/ 2 – 4 + 6 – 8 + . . . + 48 – 50

    =(2-4)+(6-8)+…+(48-50)

    =(-2)+(-2)+…+(-2)

    =(-2).13

    =-26

   4/ – 1 + 3 – 5 + 7 – . . . . + 97 – 99

   =(-1)+(3-5)+(7-9)+…+(97-99)

   =(-1)+(-2)+(-2)+…+(-2)

   =(-1)+(-2).45

   =(-1)+(-90)

   =(-91)

   5/ 1 + 2 – 3 – 4 + . . . . + 97 + 98 – 99 – 100

   =(1+2-3-4)+…+(97 + 98 – 99 – 100)

   =(-4)+…+(-4)

   =(-4).25

   =-100

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2. Bạn tham khảo :

   $1$

   $ 1 + (-2) + 3 + (-4) + . . . + 19 + (-20)$$= [1 + (-2) ]+[ 3 + (-4)] + . . . + [19 + (-20)]$

   $= (-1) + (-1) + … + (-1)$

   $= (-1) . 10$

   $= (-10)$

   $2$

   $1 – 2 + 3 – 4 + . . . + 99 – 100$

   $= (1-2)+ (3-4) + … + (99-100)$

   $= (-1) + (-1) +… + (-1)$

   $= (-1) . 50$

   $= (-50$ 

   $3$ 

   $2 – 4 + 6 – 8 + . . . + 48 – 50$

   $=( 2 – 4) + (6 – 8) + . . . + (48 – 50)$

   $= (-2) + (-2) + … + (-2)$

   $=    (-2) .12$

   $= (-24)$ 

   $4$

   $– 1 + 3 – 5 + 7 – . . . . + 97 – 99$

   $ =( -1 – 99 ) + (3 + 97) + … + (49+51)$ 

   $= -100 + 100 + …. +  100$

   $= 0 + … + 100$

   $= 100$ 

   $5$ 

   $1 + 2 – 3 – 4 + . . . . + 97 + 98 – 99 – 100$

   $=(1 + 2 – 3 – 4) + . . . . + (97 + 98 – 99 – 100)$ 

   $= (-4) + … + (-4)$

   $= (-4) .25$

   $= -100$ 

    

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