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a) x3 - x2 - 5x + 125 = ( x\(^3\) + 125 ) - ( x\(^2\) + 5x ) = ( x + 5 ) ( x\(^2\) - 5x + 25 ) - x ( x + 5 )
= ( x + 5 ) ( x\(^2\) - 5x + 25 - x ) = ( x + 5 ) ( x\(^2\) - 6x + 25 )
b) x3 + 2x2 - 6x - 27 = ( x\(^3\) - 27 ) + ( 2x\(^2\) - 6x ) = ( x - 3 ) ( x\(^2\) + 3x + 9 ) + 2x ( x - 3 )
= ( x- 3 ) ( x\(^2\) + 3x + 9 + 2x ) = ( x - 3 ) ( x\(^2\) + 5x + 9 )
c) 12x3 + 4x2 - 27x - 9 = (12x3 + 4x2 ) - ( 27x + 9 ) = 4x\(^2\)( 3x + 1 ) - 9 ( 3x + 1 )
= ( 4x\(^2\) - 9 ) ( 3x -1 ) = ( 2x - 3 ) ( 2x + 3 ) ( 3x - 1 )
i) (x2 + 8x - 34)2 - (3x2 - 8x - 2)2
= (x2 + 8x - 34- 3x\(^2\) + 8x + 2) ( x\(^2\) + 8x - 34+3x2 - 8x - 2)
= ( -2x\(^2\) + 16x - 32 ) ( 4x\(^2\) - 36 )
= ( -2x\(^2\) + 16x - 32 ) ( 2x - 6 ) ( 2x + 6 )
a, x3- x2- 5x+ 125
=- (x2+ 5x)+ (x3+125)
=-x(x+5)+ (x+5)(x2- 5x+ 25)
=(x+5)(-x+x2- 5x+ 25)
=(x+ 5)(x2- 6x+ 25)
a. x3+5x2+3x-9
= x3-x2+6x2-6x+9x-9
= x2(x-1)+6x(x-1)+9(x-1)
= (x2+6x+9)(x-1)
= (x+3)2(x-1)
b. x3+9x2+11x-21
= x3-x2+10x2-10x+21x-21
= x2(x-1)+10x(x-1)+21(x-1)
= (x2+10x+21)(x-1)
= (x+7)(x+3)(x-1)
c. x3-7x+6
= x3-x2+x2-x-6x+6
= x2(x-1)+x(x-1)-6(x-1)
= (x2+x-6)(x-1)
= (x+3)(x-2)(x-1)
d. x3-5x2+8x-4
= x3-x2-4x2+4x+4x-4
= x2(x-1)-4x(x-1)+4(x-1)
= (x2-4x+4)(x-1)
= (x-2)2(x-1)
e. x3-3x+2
= x3+2x2-2x2-4x+x+2
= x2(x+2)-2x(x+2)+(x+2)
= (x2-2x+1)(x+2)
= (x-1)2(x+2)
f. x3+8x2+17x+10
= x3+5x2+3x2+15x+2x+10
= x2(x+5)+3x(x+5)+2(x+5)
= (x2+3x+2)(x+5)
= (x+1)(x+2)(x+5)
g. x3+3x2+6x+4
= x3+x2+2x2+2x+4x+4
= x2(x+1)+2x(x+1)+4(x+1)
= (x2+2x+4)(x+1)
h. x3-2x-4
= x3-2x2+2x2-4x+2x-4
= x2(x-2)+2x(x-2)+2(x-2)
= (x2+2x+2)(x-2)
k. x3+x2+4
= x3+2x2-x2-2x+2x+4
= x2(x+2)-x(x+2)+2(x+2)
= (x2-x+2)(x+2)
l. x3-12x+7x-2
= x3+2x2-2x2-4x-x-2
= x2(x+2)-2x(x+2)-(x+2)
= (x2-2x-1)(x+2)
nhiều quá bạn ạ
hay bạn tìm hiểu cách thức chung làm dạng bài tìm GTNN chứ như thế này thì làm lâu lắm
mik chỉ tìm hiểu đc đến câu I còn lại mik k hiểu lắm, bn có lm đc k, giúp mik vs
4.a) \(2x^2-10x-3x-2x^2-26=0\)
\(-13x-26=0\Rightarrow-13\left(x+2\right)=0\)
\(\Rightarrow x=-2\)
b) \(2\left(x+5\right)-x^2-5x=0\)
\(2x+10-x^2-5x=0\Leftrightarrow-x^2-3x+10=0\)
\(-\left(x^2+3x-10\right)=0\)
\(-\left(x^2-2x+5x-10\right)=-\left(x\left(x-2\right)+5\left(x-2\right)\right)=0\)
\(-\left(x-2\right)\left(x+5\right)=0\)
\(\left\{{}\begin{matrix}x-2=0\\x+5=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=2\\x=-5\end{matrix}\right.\)
c) \(\left(2x-3\right)^2-\left(x+5\right)^2=0\)
\(\left(2x-3-x-5\right)\left(2x-3+x+5\right)=0\)
\(\left(x-8\right)\left(3x+2\right)=0\)
\(\left\{{}\begin{matrix}x-8=0\\3x+2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=8\\x=-\dfrac{2}{3}\end{matrix}\right.\)
d) \(x^3+x^2-4x-4=0\)
\(x^2\left(x+1\right)-4\left(x+1\right)=0\)
\(\left(x+1\right)\left(x^2-4\right)=\left(x+1\right)\left(x-2\right)\left(x+2\right)=0\)
\(\Rightarrow\left\{{}\begin{matrix}x+1=0\\x-2=0\\x+2=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=-1\\x=2\\x=-2\end{matrix}\right.\)
g) \(\left(x-1\right)\left(2x+3-x\right)=0\)
\(\left(x-1\right)\left(x+3\right)=0\)
\(\Rightarrow\left\{{}\begin{matrix}x-1=0\\x+3=0\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=1\\x=-3\end{matrix}\right.\)
h) \(x^2-4x+8-2x+1=x^2-6x+9=0\)
\(\left(x-3\right)^2=0\Rightarrow x=3\)
Bài 1:
a: \(6x^2-11x+3\)
\(=6x^2-9x-2x+3\)
\(=3x\left(2x-3\right)-\left(2x-3\right)\)
\(=\left(2x-3\right)\left(3x-1\right)\)
b: \(2x^2+3x-27\)
\(=2x^2+9x-6x-27\)
\(=x\left(2x+9\right)-3\left(2x+9\right)\)
\(=\left(2x+9\right)\left(x-3\right)\)
c: \(x^2-10x+24\)
\(=x^2-4x-6x+24\)
\(=x\left(x-4\right)-6\left(x-4\right)\)
\(=\left(x-4\right)\left(x-6\right)\)
d: \(49x^2+28x-5\)
\(=49x^2+28x+4-9\)
\(=\left(7x+2\right)^2-9\)
\(=\left(7x-1\right)\left(7x+5\right)\)
e: \(2x^2-5xy-3y^2\)
\(=2x^2-6xy+xy-3y^2\)
\(=2x\left(x-3y\right)+y\left(x-3y\right)\)
\(=\left(x-3y\right)\left(2x+y\right)\)