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

Toán Lớp 6: Tìm x: (x − 10) + (x − 9) + · · · + (x − 1) = −75

Toán Lớp 6: Tìm x:
(x − 10) + (x − 9) + · · · + (x − 1) = −75

Comments ( 2 )

  1. (x – 10) + (x – 9) + ….. + (x – 1) = -75
    => (x + x + …. + x) – (1 + 2 + …. + 10) = -75
    => 10x + 55 = -75
    => 10x = (-75) – 55
    => 10x = -20
    => x = (-20) : 10
    => x = -2
    Vậy x = -2

  2.    (x − 10) + (x − 9) + · · · + (x − 1) = −75
    ⇒ (x+x+x+…+x) – (1+2+3+4+5+…+10) = -75
    ⇒ 10x – 55 = -75
    ⇒ 10x        = -75 + 55
    ⇒ 10x        = -20
    ⇒     x        = -20 : 10
    ⇒     x        = -2
     

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