Toán Lớp 8: tính
a, x( 2 $x^{2}$ – 3 ) – $x^{2}$ ( 5x + 1 ) + $x^{2}$
b , 3x ( x – 2 ) – 5x . ( -1 – x ) – 8 ( $x^{2}$ – 3 )
c, $\frac{1}{2}$ $x^{2}$ ( 6x – 3 ) – x ( $x^{2}$ + $\frac{1}{2}$ ) + $\frac{1}{2}$ ( x + 4 )
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Toán Lớp 8: tính
a, x( 2 $x^{2}$ – 3 ) – $x^{2}$ ( 5x + 1 ) + $x^{2}$
b , 3x ( x – 2 ) – 5x . ( -1 – x ) – 8 ( $x^{2}$ – 3 )
c, $\frac{1}{2}$ $x^{2}$ ( 6x – 3 ) – x ( $x^{2}$ + $\frac{1}{2}$ ) + $\frac{1}{2}$ ( x + 4 )
Comments ( 2 )
$a)$ $x\left(2x^2-3\right)-x^2\left(5x+1\right)+x^2$
$=2x^3-3x-5x^2-x^2+x^2$
$=-3x^3-3x$
$b)$ $3x\left(x-2\right)-5x\left(1-x\right)-8\left(x^2-3\right)$
$=3x^2-6x-5x+5x^2-8x^2+24$
$=-11x+24$
c) 1/2 x^2(6x – 3) – x( x^2 + 1/2) (x + 4)
=x^2(3x-3/2)-(x^3+1/2x)(x+4)
=3x^3-3/2x^2-x^4-4x^3-1/2x^2-2x
=-x^4+(3x^3-4x^3)+(-3/2x^2-1/2x^2)-2x
=-x^4-x^3-2x^2-2x
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