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

Toán Lớp 8: x mũ 3 công 6x mũ 2 cộng 12x cộng 8 trừ 27y mũ 3

Toán Lớp 8: x mũ 3 công 6x mũ 2 cộng 12x cộng 8 trừ 27y mũ 3

Comments ( 2 )

  1. $ x^{3} + 6x^{2} + 12x + 8 – 27y^{3} $
    $ = x^{3} + 3 . x^{2} . 2 + 3 . x . 2^{2} + 2^{3} – 27y^{3} $
    $ = ( x + 2 )^{3} – ( 3y )^{3} $
    $ = ( x + 2 – 3y ) [ ( x + 2 )^{2} + 3y ( x + 2 ) + ( 3y )^{2} ]$
    $ = ( x – 3y + 2 ) ( x^{2} + 4x + 4 + 3xy + 6y + 9y^{2} ) $ 
     

  2. x^3 + 6x^2 + 12x + 8 – 27y^3
    = x^3 + 3x^2 . 2 + 3x . 2^2 + 2^3 – (3y)^3
    = (x + 2)^3 – (3y)^3
    = (x + 2 – 3y)[(x + 2)^2 + 3y(x + 2) + 9y^2]

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

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