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\(M=\left(x^5-2021x^4\right)-\left(x^4-2021x^3\right)+\left(x^3-2021X^2\right)-\left(x^2-2021x\right)+\left(x-2021\right)-900=-900\)
Ta có: x=2021
nên x+1=2022
Ta có: \(M=x^5-2022x^4+2022x^3-2022x^2+2022x-2921\)
\(=x^5-x^4\left(x+1\right)+x^3\left(x+1\right)-x^2\left(x+1\right)+x\left(x+1\right)-2921\)
\(=x^5-x^5-x^4+x^4+x^3-x^3-x^2+x^2+x-2921\)
\(=x-2921=-900\)
\(Q\left(x\right)=x^{101}-2020x^{100}-2022x^{99}+2022x^{98}+x-2021\)
\(=x^{100}\left(x-2021\right)+x^{99}\left(x-2021\right)-x^{98}\left(x-2021\right)+x^{98}+x-2021\)
\(Q\left(2021\right)=0+0-0+2021^{98}+0=2021^{98}\)
Lời giải:
Tại $x=2012$ thì $x-2012=0$. Ta có
$P(x)=x^5-2013x^4+2013x^3-2013x^2+2013x-2014$
$=x^4(x-2012)-x^3(x-2012)+x^2(x-2012)-x(x-2012)+(x-2012)-2$
$=(x-2012)(x^4-x^3+x^2-x+1)-2$
$=0.(x^4-x^3+x^2-x+1)-2=-2$
Cách khác:
Ta có: x=2012
nên x+1=2013
Ta có: \(P\left(x\right)=x^5-2013x^4+2013x^3-2013x^2+2013x-2014\)
\(=x^5-x^4\left(x+1\right)+x^3\left(x+1\right)-x^2\left(x+1\right)+x\left(x+1\right)-2014\)
\(=x^5-x^5-x^4+x^4+x^3-x^3-x^2+x^2+x-2014\)
\(=x-2014=2012-2014=-2\)
b: \(=1^{2020}\cdot\left(-1\right)^{2021}+4\cdot1^{2020}\cdot\left(-1\right)^{2021}-2\cdot1^{2020}\cdot\left(-1\right)^{2021}\)
\(=1\cdot\left(-1\right)+4\cdot1\cdot\left(-1\right)-2\cdot1\cdot\left(-1\right)\)
=-1-4+2
=-3
b)
Sửa đề: f(x)=A(x)+B(x)
Ta có: f(x)=A(x)+B(x)
\(=x^5+7x^4-9x^3-2x^2-\dfrac{1}{4}x-x^5+5x^4-2x^3+4x^2-\dfrac{1}{4}\)
\(=12x^4-11x^3+2x^2-\dfrac{1}{4}x-\dfrac{1}{4}\)
a) Ta có: \(A\left(x\right)=x^5-3x^2+7x^4-9x^3+x^2-\dfrac{1}{4}x\)
\(=x^5+7x^4-9x^3+\left(-3x^2+x^2\right)-\dfrac{1}{4}x\)
\(=x^5+7x^4-9x^3-2x^2-\dfrac{1}{4}x\)
Ta có: \(B\left(x\right)=5x^4-x^5+x^2-2x^3+3x^2-\dfrac{1}{4}\)
\(=-x^5+5x^4-2x^3+\left(x^2+3x^2\right)-\dfrac{1}{4}\)
\(=-x^5+5x^4-2x^3+4x^2-\dfrac{1}{4}\)
a.\(P\left(x\right)=1+3x^5-4x^2+x^5+x^3-x^2+3x^3\)
\(=1-5x^2+4x^3+4x^5\)
\(Q\left(x\right)=2x^5-x^2+4x^5-x^4+4x^2-5x\)
\(=-5x+3x^2+3x^4+2x^5\)
b.\(P\left(x\right)+Q\left(x\right)=1-5x^2+4x^3+4x^5-5x+3x^2+3x^4+2x^5\)
\(=6x^5+3x^4+4x^3-2x^2-5x+1\)
\(P\left(x\right)-Q\left(x\right)=1-5x^2+4x^3+4x^5+5x-3x^2-3x^4-2x^5\)
\(=2x^5-3x^4+4x^3-8x^2+5x+1\)
c.\(P\left(x\right)+Q\left(x\right)=6x^5+3x^4+4x^3-2x^2-5x+1\)
\(x=-1\)
\(P\left(x\right)+Q\left(x\right)=6.\left(-1\right)^5+3.\left(-1\right)^4+4.\left(-1\right)^3-5.\left(-1\right)+1\)
\(=-6+3-4+5+1=-1\)
d.\(Q\left(0\right)=\)\(-5x+3x^2+3x^4+2x^5\)
\(=0\)
\(P\left(0\right)=\)\(1-5x^2+4x^3+4x^5\)
\(=1\)
Vậy x=0 ko là nghiệm của đa thức P(x)
\(x^5-2022x^4+2020x^3+2020x^2-2020x-2021\)
=\(x^5-x^4-2021x^4+2021x^3-x^3+x^2+2021x^2-2021x+x-1-2020\)
=\(x^4\left(x-1\right)-2021x^3\left(x-1\right)-x^2\left(x+1\right)+2021x\left(x-1\right)+\left(x-1\right)-2020\)
=\(\left(x^4-2021x^3-x^2+2021x+1\right).\left(x-1\right)-2020\)
=\(\left[x^3\left(x-2021\right)-x\left(x-2021\right)+1\right]\left(x-1\right)-2020\)
=\(\left[\left(x^3-x\right).\left(x-2021\right)+1\right]\left(x-1\right)-2020\)*
vì x-2021 luôn bằng 0 \(\Rightarrow\left[\left(x^3-x\right).0+1\right]=1\)
*=1.(2021-1)-2020=0
đây nha bạn //