Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Ta có : x3 - 7x + 6
= x3 - x - 6x + 6
= x(x2 - 1) - 6(x - 1)
= x(x + 1)(x - 1) - 6(x - 1)
= (x - 1) [x(x + 1) - 6]
= (x - 1) (x2 + x - 6) .
CÁC Ý SAU TƯƠNG TỰ
a) x3 - 7x + 6
= x3 - 2x2 + 2x2 - 4x - 3x + 6
= x2 ( x - 2 ) + 2x ( x - 2 ) - 3 ( x - 2 )
= ( x - 2 ) ( x2 + 2x - 3 )
= ( x - 2 ) ( x2 - x + 3x - 3 )
= ( x - 2 ) [ x ( x - 1 ) + 3 ( x - 1 ) ]
= ( x - 2 ) ( x - 1 ) ( x + 3 )
b ) x3 - 9x2 + 6x + 16
= x3 - 8x2 - x2 + 8x - 2x + 16
= x2 ( x - 8 ) - x ( x - 8 ) - 2 ( x - 8 )
= ( x - 8 ) ( x2 - x - 2 )
= ( x - 8 ) ( x2 + x - 2x - 2 )
= ( x - 8 ) [ x ( x + 1 ) - 2 ( x + 1 ) ]
= ( x - 8 ) ( x + 1 ) ( x - 2 )
c ) x3 - 6x2 - x + 30
= x3 - 5x2 - x2 + 5x - 6x + 30
= x2 ( x - 5 ) - x ( x - 5 ) - 6 ( x - 5 )
= ( x - 5 ) ( x2 - x - 6 )
= ( x - 5 ) ( x2 - 3x + 2x - 6 )
= ( x - 5 ) [ x ( x - 3 ) + 2 ( x - 3 ) ]
= ( x - 5 ) ( x - 3 ) ( x + 2 )
d ) 2x3 - x2 + 5x + 3
= 2x3 + x2 - 2x2 - x + 6x + 3
= x2 ( 2x + 1 ) - x ( 2x + 1 ) + 3 ( 2x + 1 )
= ( 2x + 1 ) ( x2 - x + 3 )
1/ \(x^3-7x+6=0\)
\(\Leftrightarrow x^3+3x^2-3x^2-9x+2x+6=0\)
\(\Leftrightarrow x^2\left(x+3\right)-3x\left(x+3\right)+2\left(x+3\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2-3x+2\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left(x^2-x-2x+2\right)=0\)
\(\Leftrightarrow\left(x+3\right)\left[x\left(x-1\right)+2\left(x-1\right)\right]=0\)
\(\Leftrightarrow\left(x+3\right)\left(x-1\right)\left(x+2\right)=0\)
\(\Leftrightarrow\)\(x+3=0\)
hoặc \(x-1=0\)
hoặc \(x+2=0\)
\(\Leftrightarrow\)\(x=-3\)
hoặc \(x=1\)
hoặc \(x=-2\)
Vậy tập nghiệm của phương trình là : \(S=\left\{-3;1;-2\right\}\)
2/ \(x^3-6x^2-x+30\)
\(\Leftrightarrow x^3+2x^2-8x^2-16x+15x+30=0\)
\(\Leftrightarrow x^2\left(x+2\right)-8x\left(x+2\right)+15\left(x+2\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^2-8x+15\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left(x^2-3x-5x+15\right)=0\)
\(\Leftrightarrow\left(x+2\right)\left[x\left(x-3\right)-5\left(x-3\right)\right]=0\)
\(\Leftrightarrow\left(x+2\right)\left(x-3\right)\left(x-5\right)=0\)
\(\Leftrightarrow\)\(x+2=0\)
hoặc \(x-3=0\)
hoặc \(x-5=0\)
\(\Leftrightarrow\)\(x=-2\)
hoặc \(x=3\)
hoặc \(x=5\)
Vậy tập nghiệm của phương trình là :\(S=\left\{-2;3;5\right\}\)
3/ \(x^3-9x^2+6x+16=0\)
\(\Leftrightarrow x^3+x^2-10x^2-10x+16x+16=0\)
\(\Leftrightarrow x^2\left(x+1\right)-10x\left(x+1\right)+16\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x^2-10x+16\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(x^2-8x-2x+16\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left[x\left(x-8\right)-2\left(x-8\right)\right]=0\)
\(\Leftrightarrow\left(x+1\right)\left(x-8\right)\left(x-2\right)=0\)
\(\Leftrightarrow\)\(x+1=0\)
hoặc \(x-8=0\)
hoặc \(x-2=0\)
\(\Leftrightarrow\)\(x=-1\)
hoặc \(x=8\)
hoặc \(x=2\)
Vậy tập nghiệm của phương trình là :\(S=\left\{-1;8;2\right\}\)
4/ Đề bài sai ! Sửa lại nhé :
\(2x^3-x^2+5x+3=0\)
\(\Leftrightarrow2x^3+x^2-2x^2-x+6x+3=0\)
\(\Leftrightarrow x^2\left(2x+1\right)-x\left(2x+1\right)+3\left(2x-1\right)=0\)
\(\Leftrightarrow\left(2x+1\right)\left(x^2-x+3\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}2x+1=0\\x^2-x+3=0\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=-\frac{1}{2}\left(tm\right)\\\left(x-\frac{1}{2}\right)^2+\frac{11}{4}=0\left(ktm\right)\end{cases}}\)
Vậy tập nghiệm của phương trình là : \(S=\left\{-\frac{1}{2}\right\}\)
Dài 166
b) 2x2+3x-27=2x2-6x+9x-27=2x(x-3)+9(x-3)=(x-3)(2x+9)
1: \(=x^3-8x^2-x^2+8x-2x+16\)
\(=\left(x-8\right)\left(x^2-x-2\right)=\left(x-8\right)\left(x-2\right)\left(x+1\right)\)
2: \(=x^3+2x^2-8x^2-16x+15x+30\)
\(=\left(x+2\right)\left(x^2-8x+15\right)\)
\(=\left(x+2\right)\left(x-3\right)\left(x-5\right)\)
3: \(=2x^3+x^2-2x^2-x+6x+3\)
\(=\left(2x+1\right)\left(x^2-x+3\right)\)
4: \(=64x^4+16x^2y^2+y^4-16x^2y^2\)
\(=\left(8x^2+y^2\right)^2-\left(4xy\right)^2\)
\(=\left(8x^2-4xy+y^2\right)\left(8x^2+4xy+y^2\right)\)
a: \(x^3-9x^2+6x+16\)
\(=x^3-8x^2-x^2+8x-2x+16\)
\(=x^2\left(x-8\right)-x\left(x-8\right)-2\left(x-8\right)\)
\(=\left(x-8\right)\left(x^2-x-2\right)\)
\(=\left(x-8\right)\left(x-2\right)\left(x+1\right)\)
b: \(x^3-x^2-x-2\)
\(=x^3-2x^2+x^2-2x+x-2\)
\(=x^2\left(x-2\right)+x\left(x-2\right)+\left(x-2\right)\)
\(=\left(x-2\right)\cdot\left(x^2+x+1\right)\)
c: \(x^3+x^2-x+2\)
\(=x^3+2x^2-x^2-2x+x+2\)
\(=x^2\left(x+2\right)-x\left(x+2\right)+\left(x+2\right)\)
\(=\left(x+2\right)\left(x^2-x+1\right)\)
d: \(x^3-6x^2-x+30\)
\(=x^3+2x^2-8x^2-16x+15x+30\)
\(=x^2\left(x+2\right)-8x\left(x+2\right)+15\left(x+2\right)\)
\(=\left(x+2\right)\left(x^2-8x+15\right)\)
\(=\left(x+2\right)\left(x-3\right)\left(x-5\right)\)
e: Sửa đề: \(x^3-7x-6\)
\(=x^3-x-6x-6\)
\(=x\left(x^2-1\right)-6\left(x+1\right)\)
\(=x\left(x-1\right)\left(x+1\right)-6\left(x+1\right)\)
\(=\left(x+1\right)\left(x^2-x-6\right)\)
\(=\left(x+1\right)\left(x-3\right)\left(x+2\right)\)
f: \(27x^3-27x^2+18x-4\)
\(=27x^3-9x^2-18x^2+6x+12x-4\)
\(=9x^2\left(3x-1\right)-6x\left(3x-1\right)+4\left(3x-1\right)\)
\(=\left(3x-1\right)\left(9x^2-6x+4\right)\)
g: \(2x^3-x^2+5x+3\)
\(=2x^3+x^2-2x^2-x+6x+3\)
\(=x^2\left(2x+1\right)-x\left(2x+1\right)+3\left(2x+1\right)\)
\(=\left(2x+1\right)\left(x^2-x+3\right)\)
h: \(\left(x^2-3\right)^2+16\)
\(=x^4-6x^2+9+16\)
\(=x^4-6x^2+25\)
\(=x^4+10x^2+25-16x^2\)
\(=\left(x^2+5\right)^2-\left(4x\right)^2\)
\(=\left(x^2+5+4x\right)\left(x^2+5-4x\right)\)