Toán Lớp 8: Bài 1: Thực hiện phép tính:
a. 2xy(x2+ xy – 3y2) b) (4×2 – 4x – 4) : (x + 4)
c) (x3 + 3×2 – 8x – 20) : (x + 2) d) (x + 2)(3×2 – 4x)
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Toán Lớp 8: Bài 1: Thực hiện phép tính:
a. 2xy(x2+ xy – 3y2) b) (4×2 – 4x – 4) : (x + 4)
c) (x3 + 3×2 – 8x – 20) : (x + 2) d) (x + 2)(3×2 – 4x)
Comments ( 1 )
a)2xy\left( {{x^2} + xy – 3{y^2}} \right)\\
= 2{x^3}y + 2{x^2}{y^2} – 6x{y^3}\\
b)\left( {4{x^2} – 4x – 4} \right):\left( {x + 4} \right)\\
= \left( {4{x^2} + 16x – 20x – 80 + 76} \right):\left( {x + 4} \right)\\
= \left[ {\left( {x + 4} \right)\left( {4x – 20} \right) + 76} \right]:\left( {x + 4} \right)\\
= 4x – 20\,du\,76\\
c)\left( {{x^3} + 3{x^2} – 8x – 20} \right):\left( {x + 2} \right)\\
= \left( {{x^3} + 2{x^2} + {x^2} + 2x – 10x – 20} \right):\left( {x + 2} \right)\\
= \left( {x + 2} \right)\left( {{x^2} + x – 10} \right):\left( {x + 2} \right)\\
= {x^2} + x – 10\\
d)\left( {x + 2} \right)\left( {3{x^2} – 4x} \right)\\
= 3{x^3} – 4{x^2} + 6{x^2} – 8x\\
= 3{x^3} + 2{x^2} – 8x
\end{array}$