Bài1: a) xy.( x2 – 2y) b) x.(x + 3) c) 5xy(5-2x) d) 5x(x2+3xy-1) Bài2: a) (x-5)(3x+1) b) 4x(x-5) +(2x-4)(x + 3) c) ( x 3)(x+

1 bình luận về “Bài1: a) xy.( x2 – 2y) b) x.(x + 3) c) 5xy(5-2x) d) 5x(x2+3xy-1) Bài2: a) (x-5)(3x+1) b) 4x(x-5) +(2x-4)(x + 3) c) ( x 3)(x+”

1. Giải đáp:$\begin{array}{l}
   1)a){x^3}y – 2x{y^2}\\
   b){x^2} + 3x\\
   c)25xy – 10{x^2}y\\
   d)5{x^3} + 15{x^2}y – 5x\\
   2)a)3{x^2} – 14x – 5\\
   b)6{x^2} – 18x – 12\\
   c)3{x^2} + 6x – 9\\
   d) – 3x + 7
   \end{array}$

    

   Lời giải và giải thích chi tiết:

   $\begin{array}{l}
   1)a)xy\left( {{x^2} – 2y} \right)\\
    = xy.{x^2} – xy.2y\\
    = {x^3}y – 2x{y^2}\\
   b)x\left( {x + 3} \right)\\
    = x.x + x.3\\
    = {x^2} + 3x\\
   c)5xy\left( {5 – 2x} \right)\\
    = 5xy.5 – 5xy.2x\\
    = 25xy – 10{x^2}y\\
   d)5x\left( {{x^2} + 3xy – 1} \right)\\
    = 5x.{x^2} + 5x.3xy – 5x\\
    = 5{x^3} + 15{x^2}y – 5x\\
   2)a)\left( {x – 5} \right)\left( {3x + 1} \right)\\
    = 3{x^2} + x – 15x – 5\\
    = 3{x^2} – 14x – 5\\
   b)4x\left( {x – 5} \right) + \left( {2x – 4} \right)\left( {x + 3} \right)\\
    = 4{x^2} – 20x + 2{x^2} + 6x – 4x – 12\\
    = 6{x^2} – 18x – 12\\
   c)\left( {x – 3} \right)\left( {x + 3} \right) + 2x\left( {x + 3} \right)\\
    = {x^2} – {3^2} + 2{x^2} + 6x\\
    = 3{x^2} + 6x – 9\\
   d)\left( {x – 1} \right)\left( {x – 4} \right) – \left( {x – 3} \right)\left( {x + 1} \right)\\
    = {x^2} – 4x – x + 4 – \left( {{x^2} + x – 3x – 3} \right)\\
    = {x^2} – 5x + 4 – \left( {{x^2} – 2x – 3} \right)\\
    = {x^2} – 5x + 4 – {x^2} + 2x + 3\\
    =  – 3x + 7
   \end{array}$

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