giải phương trình (×+1)/2020+(×-1)/2018=(×+5)/2024+(x-5)/2014
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\(\Leftrightarrow\left(\dfrac{x+1}{2022}+1\right)+\left(\dfrac{x+3}{2020}+1\right)+\left(\dfrac{x+5}{2018}+1\right)+\left(\dfrac{x+7}{2016}+1\right)=0\)
=>x+2023=0
=>x=-2023
\(\dfrac{1}{x+1}\)-\(\dfrac{5}{x-2}\)=\(\dfrac{15}{\left(x+1\right)\left(x-2\right)}\)
\(\Leftrightarrow\)\(\dfrac{x-2}{\left(x+1\right)\left(x-2\right)}\)-\(\dfrac{5\left(x+1\right)}{\left(x+1\right)\left(x-2\right)}\)=\(\dfrac{15}{\left(x+1\right)\left(x-2\right)}\)
\(\Leftrightarrow\)x-2-5(x+1)=15
\(\Leftrightarrow\) x-2-5x-5=15
\(\Leftrightarrow\)x-5x=15+2+5
\(\Leftrightarrow\)-4x=22
\(\Leftrightarrow\)x=-\(\dfrac{11}{2}\)
vậy
\(\frac{x-2}{2017}+\frac{x-3}{2018}=\frac{x-4}{2019}+\frac{x-5}{2020}\)
<=> \(\frac{x-2}{2017}+1+\frac{x-3}{2018}+1=\frac{x-4}{2019}+1+\frac{x-5}{2020}+1\)
<=> \(\frac{x+2015}{2017}+\frac{x+2015}{2018}-\frac{x+2015}{2019}-\frac{x+2015}{2020}=0\)
<=> \(\left(x+2015\right)\left(\frac{1}{2017}+\frac{1}{2018}-\frac{1}{2019}-\frac{1}{2020}\right)=0\)
<=> x + 2015 = 0 ( vì \(\frac{1}{2017}+\frac{1}{2018}-\frac{1}{2019}-\frac{1}{2020}\ne0\))
<=> x = - 2015
Vậy x = -2015.
Giải phương trình :
\(\frac{x-2}{2017}+\frac{x-3}{2018}=\frac{x-4}{2019}+\frac{x-5}{2020}\)
\(\Rightarrow\frac{x-2}{2017}+1+\frac{x-3}{2018}+1=\frac{x-4}{2019}+1+\frac{x-5}{2020}+1\)
\(\Rightarrow\frac{x+2015}{2017}+\frac{x+2015}{2018}-\frac{x+2015}{2019}-\frac{x+2015}{2020}=0\)
\(\Rightarrow\left(x+2015\right)\left(\frac{1}{2017}+\frac{1}{2018}-\frac{1}{2019}-\frac{1}{2020}\right)=0\)
Mà \(\left(\frac{1}{2017}+\frac{1}{2018}-\frac{1}{2019}-\frac{1}{2020}\right)>0\)
\(\Rightarrow x+2015=0\)
\(\Rightarrow x=-2015\)
Ta có:\(\frac{x-2}{2017}+1+\frac{x-3}{2018}+1=\frac{x-4}{2019}+1+\frac{x-5}{2020}+1\)
\(\Rightarrow\frac{x+2015}{2017}+\frac{x+2015}{2018}-\frac{x+2015}{2019}-\frac{x+2015}{2020}=0\)
\(\Rightarrow\left(x+2015\right)\left(\frac{1}{2017}+\frac{1}{2018}-\frac{1}{2019}-\frac{1}{2020}\right)=0\)
Mà \(\frac{1}{2017}+\frac{1}{2018}-\frac{1}{2019}-\frac{1}{2020}>0\)
\(\Rightarrow x+2015=0\Rightarrow x=-2015\)
\(S=\left\{-2015\right\}\)
Nhận thấy vế trái luôn dương nên \(x-2020\ge0\Leftrightarrow x\ge2020\)
Với \(x\ge2020\Rightarrow\left\{{}\begin{matrix}x-2017\ge0\\2x-2018\ge0\\3x-2019\ge0\end{matrix}\right.\)
PT trở thành: \(x-2017+2x-2018+3x-2019=x-2020\)
Hay kết hợp với điều kiện \(x=\dfrac{4034}{5}\) suy ra PT đã cho vô nghiệm
Bài làm:
Pt <=> \(\left(\frac{x-1}{2020}-1\right)+\left(\frac{x-3}{2018}-1\right)+\left(\frac{x-5}{2016}-1\right)+\left(\frac{x-7}{2014}-1\right)=4-4\)
\(\Leftrightarrow\frac{x-2021}{2020}+\frac{x-2021}{2018}+\frac{x-2021}{2016}+\frac{x-2021}{2014}=0\)
\(\Rightarrow x-2021=0\Rightarrow x=2021\)
\(\left(x-2018\right)^3+\left(x-2020\right)^3=\left(2x-4038\right)\)
\(\Leftrightarrow\left(x-2018\right)^3+\left(x-2020\right)^3+\left(4038-2x\right)^3=0^{^{\left(1\right)}}\)
Áp dụng bđt \(a+b+c=0\Leftrightarrow a^3+b^3+c^3=3abc\)
Ta có \(\left(x-2018\right)+\left(x-2020\right)+\left(4038-2x\right)=0\)
\(\Leftrightarrow\left(x-2018\right)^3+\left(x-2020\right)^3+\left(4038-2x\right)^3=3\left(x-2018\right)\left(x-2020\right)\left(4038-2x\right)\)
Do đó (1) \(\Leftrightarrow3\left(x-2018\right)\left(x-2020\right)\left(4038-x\right)=0\)
<=> x-2018 =0 hoặc x-2020 = 0 hoặc 4038 -2x =0
<=> x=2018 hoặc x=2020 hoặc x=2019
Vậy phương trình đã cho có nghiệm S={2018;2020;2019}
\(\left(x-2018\right)^3+\left(x-2020\right)^3=\left(2x-4038\right)^3\)
\(\Leftrightarrow\left(x-2018\right)^3+\left(x-2020\right)^3+\left(4038-2x\right)^3=0\)
ta có \(\left(x-2018\right)+\left(x-2020\right)+\left(4038-2x\right)=0\)
nên đặt \(\left(x-2018\right)=a;\left(x-2020\right)=b;\left(4038-2x\right)=c\Leftrightarrow a+b+c=0\)
Khi đó a3 + b3+c3 = 0 ( 1)
mà a+b+c=0 \(\Leftrightarrow\)a+b=-c
\(\Leftrightarrow\)(a+b)3 = -c3
\(\Leftrightarrow\)a3+b3+c3 = 3abc (2)
Từ (1) và (2) \(\Leftrightarrow\)abc=0
\(\Leftrightarrow\)\(\left(x-2018\right)=0hoặc\left(x-2020\right)=0hoặc\left(4038-2x\right)=0\)
\(\Leftrightarrow\)\(x=2018hoặcx=2020hoặcx=2019\)
Vậy tập nghiệm của PT là S={2018;2019;2020}
\(\dfrac{x+1}{2020}+\dfrac{x-1}{2018}=\dfrac{x+5}{2024}+\dfrac{x-5}{2014}\)
\(\Leftrightarrow\left(\dfrac{x+1}{2020}-1\right)+\left(\dfrac{x-1}{2018}-1\right)-\left(\dfrac{x+5}{2024}-1\right)-\left(\dfrac{x-5}{2014}-1\right)=0\)
\(\Leftrightarrow\dfrac{x-2019}{2020}+\dfrac{x-2019}{2018}-\dfrac{x-2019}{2024}-\dfrac{x-2019}{2014}=0\)
\(\Leftrightarrow\left(x-2019\right)\left(\dfrac{1}{2020}+\dfrac{1}{2018}-\dfrac{1}{2024}-\dfrac{1}{2014}\right)=0\)
\(\Leftrightarrow x-2019=0\\ \Leftrightarrow x=2019\)