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

Toán Lớp 7: cho 3x-2y/4=2z-4x/3=4y-3z/2 chung minh rang x/2=y/3=z/4

Toán Lớp 7: cho 3x-2y/4=2z-4x/3=4y-3z/2 chung minh rang x/2=y/3=z/4

Comments ( 2 )

  1. (3x-2y)/4 = (2z-4x)/3 = (4y-3z)/2 =

    = (12x-8y)/16 = (6z-12x)/9 = (8y-6z)/4 = (12x-8y + 6z-12x + 8y-6z)/(16+9+4) = 0
    <=>
    {12x – 8y = 0
    {6z – 12x = 0
    {8y – 6z = 0
    <=>
    {x/2 = y/3
    {z/4 = x/2
    {y/3 = z/4

    <=> x/2 = y/3 = z/4

     

  2. (3x-2y)/4 = (2z-4x)/3 = (4y-3z)/2
    => (12x-8y)/16 = (6z – 12x)/9 = (8y – 6z)/4
    Áp dụng tính chất của dãy tỉ số bằng nhau ta được:
    (12x-8y)/16 = (6z – 12x)/9 = (8y – 6z)/4 = (12x-8y + 6z-12x + 8y-6z)/(16+9+4) = 0/29 =0
    => 12x – 8y = 0 => 3x – 2y = 0 => 3x = 2y => x/ 2 = y/3
    6z-12x = 0 => 2z – 4x = 0 => 2z = 4x => x/2 = z/4
    => x/2 = y/3=z/4 (ĐPCM)

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

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