Làm Tính Chia
(-X^2+6X^3 -26X+21): (2X-3)
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\(=\left(6x^3-x^2-26x+21\right):\left(3-2x\right)\\ =\left(6x^3-9x^2+8x^2-12x-14x+21\right):\left(3-2x\right)\\ =\left(2x-3\right)\left(3x^2+4x-7\right):\left(3-2x\right)\\ =-\left(3x^2+4x-7\right)=-3x^2-4x+7\)
\(1.\) Phân tích đa thức thành nhân tử
\(4-32x^3=-\left(32x^3-4\right)=\left(-4\right)\left(8x^3-1\right)=\left(-4\right)\left(2x-1\right)\left(4x^2+2x+1\right)\)
\(2.\) Thực hiện phép tính
Ta có: \(-x^2+6x^3-26x+21=6x^3-x^2-26x+21=\left(x-1\right)\left(2x-3\right)\left(3x+7\right)\)
Do đó:
\(\frac{-x^2+6x^3-26x+21}{2x-3}=\frac{\left(x-1\right)\left(2x-3\right)\left(3x+7\right)}{2x-3}=\left(x-1\right)\left(3x+7\right)=3x^2+4x-7\)
a) 6x3 + 3x2 + 4x + 2
= ( 6x3 + 3x2 ) + ( 4x + 2 )
= 3x2( 2x + 1 ) + 2( 2x + 1 )
= ( 2x + 1 )( 3x2 + 2 )
=> ( 6x3 + 3x2 + 4x + 2 ) : ( 3x2 + 2 ) = 2x + 1
b) 2x3 - 26x - 24
= 2( x3 - 13x - 12 )
= 2( x3 + 4x2 - 4x2 + 3x - 16x - 12 )
= 2[ ( x3 + 4x2 + 3x ) - ( 4x2 + 16x + 12 ) ]
= 2[ x( x2 + 4x + 3 ) - 4( x2 + 4x + 3 ) ]
= 2( x2 + 4x + 3 )( x - 4 )
=> ( 2x3 - 26x - 24 ) : ( x2 + 4x + 3 ) = 2( x - 4 ) = 2x - 8
c) x3 - 7x + 6
= x3 - 3x2 + 3x2 + 2x - 9x - 6
= ( x3 - 3x2 + 2x ) + ( 3x2 - 9x + 6 )
= x( x2 - 3x + 2 ) + 3( x2 - 3x + 2 )
= ( x2 - 3x + 2 )( x + 3 )
=> ( x3 - 7x + 6 ) : ( x + 3 ) = x2 - 3x + 2
a,\(\left(6x^3+3x^2+4x+2\right)\div\left(3x^2+2\right)\)
\(=\left[3x^2\left(2x+1\right)+2\left(2x+1\right)\right]\div\left(3x^2+2\right)\)
\(=\left[\left(3x^2+2\right)\left(2x+1\right)\right]\div\left(3x^2+2\right)\)
\(=2x+1\)
Tim x,
a,2x^4-6x^3+x^2+6x-3=0
b,x^3-9x^2+26x+24=0
c, P= 2x^4 - 4x^3 + 6x^2 - 4x + 5 biet rang x^2 - x=7
a)\(2x^4-6x^3+x^2+6x-3=0\)
\(\Leftrightarrow2x^4-6x^3+3x^2-2x^2+6x-3=0\)
\(\Leftrightarrow x^2\left(2x^2-6x+3\right)-\left(2x^2-6x+3\right)=0\)
\(\Leftrightarrow\left(x^2-1\right)\left(2x^2-6x+3\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)\left(2x^2-6x+3\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x-1=0\\x+1=0\\2x^2-6x+3=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=1\\x=-1\\\Delta_{2x^2-6x+3}=\left(-6\right)^2-4\left(2.3\right)=12\end{array}\right.\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=1\\x=-1\\x_{1,2}=\frac{6\pm\sqrt{12}}{4}\end{array}\right.\)
b)\(x^3+9x^2+26x+24=0\)
\(\Leftrightarrow x^3+5x^2+6x+4x^2+20x+24=0\)
\(\Leftrightarrow x\left(x^2+5x+6\right)+4\left(x^2+5x+6\right)=0\)
\(\Leftrightarrow\left(x^2+5x+6\right)\left(x+4\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x+3\right)\left(x+4\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x+2=0\\x+3=0\\x+4=0\end{array}\right.\)\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-2\\x=-3\\x=-4\end{array}\right.\)
\(=\dfrac{6x^3-9x^2+8x^2-12x-14x+21}{2x-3}=3x^2+4x-7\)