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

Toán Lớp 8: cho a+b+c=2x chứng minh a ²-b ²-c ²+2bc=4(x-b)(x-c)

Toán Lớp 8: cho a+b+c=2x chứng minh a ²-b ²-c ²+2bc=4(x-b)(x-c)

Comments ( 1 )

  1.  Ta có:
    VT=a^2-b^2-c^2+2bc
    =a^2-(b^2+c^2-2bc)
    =a^2-(b-c)^2
    =(a-b+c)(a+b-c)
    =(2x-2b)(2x-2c)
    =4(x-b)(x-c)
    =VP
    Vậy đẳng thức được chứng minh
    —————————————
    2x-2b=a+b+c-2b=a-b+c
    2x-2c=a+b+c-2c=a+b-c

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