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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 6: Bài 3: a/Tính tổng sau bằng 1 cách hợp lí : A=10/11.16+10/16.21+10/21.26+…+10/61.66 b/tìm UCLN(123456789,987654321)

Toán Lớp 6: Bài 3:
a/Tính tổng sau bằng 1 cách hợp lí :
A=10/11.16+10/16.21+10/21.26+…+10/61.66
b/tìm UCLN(123456789,987654321)

Comments ( 2 )

  1. A=10/11.16+10/16.21+10/21.26+…+10/61.66
    A=2.(5/(11.16) + 5/(16.21) + 5/(21.26) +…+ 5/(61.66))
    A = 2.(1/11  – 1/16 + 1/16 – 1/21 + 1/21 – 1/26 +…+ 1/61 – 1/66)
    A=2.(1/11 – 1/66)
    A=2. 5/66
    A=5/33
    b/
    Ư(123456789) = {\pm1;\pm3;\pm9;\pm123456789}
    Ư(987654321)={\pm1;\pm3;\pm9;\pm987654321}
    => ƯCLN = {\pm9}

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222-9+11+12:2*14+14 = ? ( )