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Rút gọn
\(\left(2x+1\right)\left(4x^2-3x+1\right)+\left(2x-1\right)\left(4x^2+3x+1\right)\)
\(=8x^3-12x^2+2x+4x^2-3x+1+8x^3+12x^2+2x-4x^2-3x-1\)
\(=16x^3-2x\)
Phân tích đa thức thnahf nhân tử
\(4y^2+16y-x^2-8x\)
\(=\left(4y^2-x^2\right)+\left(16y-8x\right)\)
\(=\left(2y-x\right)\left(2y+x\right)+8\left(2y-x\right)\)
\(=\left(2y-x\right)\left(2y+x+8\right)\)
Chứng minh .............
Có: \(x^2+x+1=\left(x^2+2\cdot x\cdot\frac{1}{2}+\frac{1}{4}\right)+\frac{3}{4}=\left(x+\frac{1}{2}\right)^2+\frac{3}{4}\)
Vì: \(\left(x+\frac{1}{2}\right)^2\ge0\)
=> \(\left(x+\frac{1}{2}\right)^2+\frac{3}{4}>0\)
Kết luận......
bài 1
a)\(x^2+5x+6=\left(x+2\right)\left(x+3\right)=0\Leftrightarrow\orbr{\begin{cases}x+3=0\\x+2=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=-3\\x=-2\end{cases}}}\)
Hướng dẫn thôi :
a) x ( x + 2 ) ( x^2 - 6x + 4 )
b) ( x + 1 ) ( x + 2 ) ( x - 2 )
a)\(2x^2-3x-2\)
\(=2x^2+x-4x-2\)
\(=x\left(2x+1\right)-2\left(2x+1\right)\)
\(=\left(x-2\right)\left(2x+1\right)\)
b)\(3x^2+x-2\)
\(=3x^2-2x+3x-2\)
\(=x\left(3x-2\right)+\left(3x-2\right)\)
\(=\left(x+1\right)\left(3x-2\right)\)
c)\(4x^2-7x-2\)
\(=4x^2+x-8x-2\)
\(=x\left(4x+1\right)-2\left(4x+1\right)\)
\(=\left(x-2\right)\left(4x+1\right)\)
d)\(4x^2+5x-6\)
\(=4x^2-3x+8x-6\)
\(=x\left(4x-3\right)+2\left(4x-3\right)\)
\(=\left(x+2\right)\left(4x-3\right)\)
ý 1:
2x2-3x-2=2x2-4x+x-2=2x(x-2)+(x-2)=(x-2)(2x+1)
ý 2:
3x2+x-2=3x2+3x-2x-2=(3x2+3x)-(2x+2)=3x(x+1)-2(x+1)=(x+1)(3x-2)
ý 3:
4x2-7x-2=4x2-8x+x-2=(4x2-8x)+(x-2)=4x(x-2)+(x-2)=(x-2)(4x+1)
ý 4:
4x2+5x-6=4x2+8x-3x-6=(4x2+8x)-(3x+6)=4x(x+2)-3(x+2)=(x+2)(4x-3)
a) \(x^2+5x+6=x^2+2x+3x+6=x\left(x+2\right)+3\left(x+2\right)=\left(x+3\right)\left(x+2\right)\)
b) \(x^2-4x+3=x^2-x-3x+3=x\left(x-1\right)-3\left(x-1\right)=\left(x-3\right)\left(x-1\right)\)
c) \(x^2+5x+4=x^2+x+4x+4=x\left(x+1\right)+4\left(x+1\right)=\left(x+4\right)\left(x+1\right)\)
d) \(x^2-x-6=x^2+2x-3x-6=x\left(x+2\right)-3\left(x+2\right)=\left(x-3\right)\left(x+2\right)\)
\(b,x^2+4x+3=x^2+3x+x+3.\)
\(=x\left(x+3\right)+\left(x+3\right)=\left(x+1\right)\left(x+3\right)\)
\(c,16x-5x^2-3=x-5x^2+15x-3\)
\(=x\left(1-5x\right)+3\left(5x-1\right)\)
\(=\left(x+3\right)\left(1-5x\right)\)
\(d,x^4+4=x^4+4x^2+4-4x^2=\left(x+2\right)^2-4x^2\)
\(=\left(x^2+2-2x\right)\left(x^2+2+2x\right)\)
\(x^4+x^3+2x^2+x+1\)
\(=\left(x^4+2x^2+1\right)+\left(x^3+x\right)\)
\(=\left(x^2+1\right)^2+x\left(x^2+1\right)\)
\(=\left(x^2+1\right)\left(x^2+1+x\right)\)
x^4+x^3+2x^2+x+1
=(x^4+2x^2+1)+(x^3+x)
=(x^2+1)^2+x(x^2+1)
=(x^2+1)(x^2+x+1)
Phân tích đa thức thành nhân tử:
a) \(3a^2-3ab+9b-9a=3a\left(a-b\right)+9\left(b-a\right)=3\left(a-b\right)\left(a-3\right)\)
b) \(2xm^3-2m=2m\left(xm^2-1\right)\)
c) \(x^2-5x+6=x^2-2x-3x+6=x\left(x-2\right)-3\left(x-2\right)=\left(x-2\right)\left(x-3\right)\)
Tìm x:
a) \(8x^2+10x+3=0\)
\(\Leftrightarrow8x^2+12x-2x-3=0\Leftrightarrow4x\left(2x+3\right)-\left(2x+3\right)=0\)
\(\Leftrightarrow\left(2x+3\right)\left(4x-1\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=-\frac{3}{2}\\x=\frac{1}{4}\end{array}\right.\)
b) \(x^4-2x^3+10x^2-20x=0\)
\(\Leftrightarrow x^3\left(x-2\right)+10x\left(x-2\right)=0\)
\(\Leftrightarrow x\left(x-2\right)\left(x^2+10\right)=0\)
\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x-2=0\end{array}\right.\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x=2\end{array}\right.\)
\(3x^6-4x^5+2x^4-8x^3+2x^2-4x+3\)
\(=3x^6+3x^4-4x^5-4x^3-x^4-x^2-4x^3-4x+3x^2+3\)
\(=\left(x^2+1\right)\left(3x^4-4x^3-x^2-4x+3\right)\)
\(=\left(x^2+1\right)\left(x^2+x+1\right)\left(3x^2-7x+3\right)\)