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

Toán Lớp 8: a)(x-2)(x+3)-x(x+1) b)3x^3-27x c)x^2+4y^2-3x+6y-4xy

Tháng Sáu 21, 2022 Toán học 2 Comments 0 views

Toán Lớp 8: a)(x-2)(x+3)-x(x+1)
b)3x^3-27x
c)x^2+4y^2-3x+6y-4xy

Comments ( 2 )

  1. tuyen98
    tuyen98
    21 Tháng Sáu, 2022 at 4:18 chiều
    Reply
    #andy
    \[\begin{array}{l}
    a)\left( {x – 2} \right)\left( {x + 3} \right) – x\left( {x + 2} \right)\\
     = {x^2} + 3x – 2x – 6 – {x^2} – 2x\\
     = \left( {3x – 2x – 2x} \right) – 6\\
     =  – x – 6\\
    b)3{x^3} – 27x\\
     = 3x.\left( {{x^2} – 9} \right)\\
     = 3x\left( {x – 3} \right)\left( {x + 3} \right)\\
    c){x^2} + 4{y^2} – 3x + 6y – 4xy\\
     = {x^2} – 4xy + 4{y^2} – 3x + 6y\\
     = \left( {{x^2} – 4xy + 4{y^2}} \right) – \left( {3x – 6y} \right)\\
     = {\left( {x – 2y} \right)^2} – 3\left( {x – 2y} \right)\\
     = \left( {x – 2y} \right)\left( {x – 2y – 3} \right)
    \end{array}\]

  2. baoquyen
    baoquyen
    21 Tháng Sáu, 2022 at 4:17 chiều
    Reply
    Giải đáp:
    a)
    (x-2)(x+3)-x(x+2)
    =x^(2)+3x-2x-6-x^(2)-2x
    =(x^(2)-x^2)+(3x-2x-2x)-6
    =-x-6
    b)
    3x^(3)-27x
    =3x.x^(2)-3x.9
    =3x.(x^(2)-9)
    =3x.(x^(2)-3^2)
    =3x.(x-3)(x+3)
    c)
    x^(2)+4y^(2)-3x+6y-4xy
    =x^(2)-4xy+4y^(2)-3x+6y
    =[x^(2)-2.x.2y+(2y)^2]-(3x-6y)
    =(x-2y)^(2)-3(x-2y)
    =(x-2y)(x-2y-3)

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

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