Tính; a)20-19+18-17+16-15+……..+4-3+2-1=? b)1+2-3+4-5+6-7+………+18-19+20=?

Question

Tính;
a)20-19+18-17+16-15+……..+4-3+2-1=?
b)1+2-3+4-5+6-7+………+18-19+20=?

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Natalia 2 tháng 2021-10-10T15:06:36+00:00 2 Answers 12 views 0

Answers ( )

    0
    2021-10-10T15:08:09+00:00

    a,20-19+18-17+16-15+……..+4-3+2-1=(20-19)+(18-17)+(16-15)+……..+(4-3)+(2-1)

    =1+1+1+1+…+1

    =20

    b)1+2-3+4-5+6-7+………+18-19+20

    =0

    0
    2021-10-10T15:08:32+00:00

    Đáp án:

     a) 20-19+18-17+16-15+14-13+12-11+10-9+8-7+6-5+4-3+2-1=10

     b) 1+2-3+4-5+6-7+8-9+10-11+12-13+14-15+16-17+18-19+20=12

     

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