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ta có x4+2010x2+2009x+2010=0
suy ra x4-x+2010x+2010x2+2010=0
x(x3-1)+2010(x2+x+1)=0
x(x-1)(x2+x+1)+2010(x2+x+1)=0
(x2+x+1)(x2-x+2010)=0
hoặc x2+x+1=0
x2-x+2020=0
mà x2+x+1>0, x2-x+2020>0
Vậy không tồn tại x thỏa mãn đề bài
\(x^4+2010x^2+2009x+2010\\ =\left(x^4-x\right)+\left(2010x^2+2010x+2010\right)\\ =x\left(x^3-1\right)+2010\left(x^2+x+1\right)\\ =x\left(x-1\right)\left(x^2+x+1\right)+2010\left(x^2+x+1\right)\\ =\left(x^2+x+1\right)\left(x^2-x+2010\right)\)
\(x^4+2010x^2+2009x+2010\)
\(=\left(x^4-x\right)+\left(2010x^2+2010x+2010\right)\)
\(=x\left(x^3-1\right)+2010\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2010\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-x+2010\right)\)
\(x^4+2010x^2+2009x+2010\)
\(=\left(x^4-x\right)+2010\left(x^2+x+1\right)\)
\(=x\left(x^3-1\right)+2010\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2010\left(x^2+x+1\right)\)
\(=\left(x^2-x+2010\right)\left(x^2+x+1\right)\)
-Ta thấy \(x^4+x^2+1=x^4-x+x^2+x+1=\left(x^2-x\right)\left(x^2+x+1\right)+\left(x^2+x+1\right)=\left(x^2-x+1\right)\left(x^2+x+1\right)\)
Vậy PT sẽ thành
\(\frac{2010x\left(x^3+1\right)}{x\left(x^4+x^2+1\right)}+\frac{2010x\left(x^3-1\right)}{x\left(x^4+x^2+1\right)}=\frac{2011}{x\left(x^4+x^2+1\right)}\)
\(\Leftrightarrow2.2010x^4=2011\Leftrightarrow x=...\)
Bài \(1.\)
\(x^4+2010x^2+2009x+2010=\left(x^4-x\right)+\left(2010x^2+2010x+2010\right)\)
\(=x\left(x^3-1\right)+2010\left(x^2+x+1\right)\)
\(=x\left(x-1\right)\left(x^2+x+1\right)+2010\left(x^2+x+1\right)\)
\(=\left(x^2+x+1\right)\left(x^2-x+2010\right)\)
Bài \(2.\)
\(x^2-25=y\left(y+6\right)\)
\(\Leftrightarrow\) \(x^2-25+9=y^2+6y+9\)
\(\Leftrightarrow\) \(x^2-16=\left(y+3\right)^2\)
\(\Leftrightarrow\) \(x^2-\left(y+3\right)^2=16\)
\(\Leftrightarrow\) \(\left(x-y-3\right)\left(x+y+3\right)=16\)
Bạn xét từng trường hợp nhóe!
a) (x+y+z)3 -x3 - y3 - z3
= [(x + y + z) - z][(x+ y + z)2 + x2 + x(x+ y + z)] - (y + z)(y2+ z2 - yz)
= (y+z)(x2 + y2 + z2 + 2xy + 2yz + 2xz + 2x2 + xy + xz) - (y + z)( y2+ z2 - yz)
= (y+z)(x2 + y2 + z2 + 2xy + 2yz + 2xz + 2x2 + xy + xz - y2+ z2 - yz)
= (y+z)(3x2 + 3xy + 3yz + 3xz )
= 3(y+z)(x2 + xy + yz + xz )
= 3(y+z)[x(x+y) + z(x+y)]
= 3(x+y)(y+z)(x+z)
b) x4 + 2010x2 + 2009x + 2010
= x4 +x2 +1 + 2009x2 + 2009x + 2009
= (x4 + 2x2 +1 -x2) + 2009(x2 +x +1)
= ( x2 +1 )2 -x2 + 2009(x2 +x +1)
= (x2 +x +1)(x2 -x +1) + 2009(x2 +x +1)
= (x2 +x +1)(x2 -x +1+2009)
= (x2 +x +1)(x2 -x +2010)
a)
x4+2010x2+2009x+2010
= (x4-x)+(2010x2+2010x+2010)
= x(x3-1)+2010(x2+x+1)
= x(x-1)(x2+x+1) +2010(x2+x+1)
= (x2+x+1)(x2-x+2010)
b)
x3-x2-5x+21
= x3+3x2-4x2-12x+7x+21
= x2(x+3)-4x(x+3)+7(x+3)
= (x+3)(x2-4x+7)
\(\Leftrightarrow x^4-x+2010\left(x^2+x+1\right)=0\)
\(\Leftrightarrow x\left(x-1\right)\left(x^2+x+1\right)+2010\left(x^2_{ }+x+1\right)=0\)
\(\Leftrightarrow\left(x^2-x+2010\right)\left(x^2+x+1\right)=0\left(1\right)\)
Ta có \(\left\{{}\begin{matrix}x^2-x+2010=\left(x-\frac{1}{2}\right)^2+\frac{8039}{4}>0\\x^2+x+1=\left(x+\frac{1}{2}\right)^2+\frac{3}{4}>0\end{matrix}\right.\)
Nên PT vô gnhiệm