\(\dfrac{2021x13+2007+2020x2007}{2020+2020x520+1500x2020}\)
K
Khách
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Những câu hỏi liên quan
DN
1
NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
6 tháng 5 2023
B = \(\dfrac{2021\times13+2007+2020\times2007}{2020+2020\times520+1500\times2020}\)
B = \(\dfrac{2021\times13+2007\times\left(1+2020\right)}{2020\times\left(1+520+1500\right)}\)
B = \(\dfrac{2021\times13+2007\times2021}{2020\times2021}\)
B = \(\dfrac{2021\times\left(13+2007\right)}{2021\times2020}\)
B = \(\dfrac{2021\times2020}{2021\times2020}\)
B = 1
YO
1
22 tháng 7 2020
B=2021 x 13 + 2009 + 2020 x 2007/2020 + 2020 x520x2020
B=2021 x 13 +2009+2020/1x2007/2020 +2020x520x2020
B=26273+2009+20201/1x2007/20201+2121808000
B=28282+2007+2121808000
B=2121838289
KW
0
12 tháng 1 2018
Ta có: \(\dfrac{1}{x}+\dfrac{1}{y}+\dfrac{1}{z}=\dfrac{1}{x+y+z}\)
\(\Leftrightarrow\dfrac{xy+yz+xz}{xyz}=\dfrac{1}{x+y+z}\)
\(\Leftrightarrow\left(xy+yz+xz\right)\left(x+y+z\right)=xyz\)
\(\Leftrightarrow x^2y+xy^2+y^2z+yz^2+x^2z+xz^2+3xyz-xyz=0\)
\(\Leftrightarrow x^2y+xy^2+y^2z+yz^2+x^2z+xz^2+2xyz=0\)
\(\Leftrightarrow x^2y+xy^2+x^2z+xyz+y^2z+yz^2+xz^2+xyz=0\)
\(\Leftrightarrow x\left(xy+y^2+xz+yz\right)+z\left(y^2+yz+xz+xy\right)=0\)
\(\Leftrightarrow x\left[y\left(x+y\right)+z\left(x+y\right)\right]+z\left[y\left(y+z\right)+x\left(y+z\right)\right]=0\)
\(\Leftrightarrow x\left(x+y\right)\left(y+z\right)+z\left(y+z\right)\left(x+y\right)=0\)
\(\Leftrightarrow\left(x+y\right)\left(y+z\right)\left(z+x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x+y=0\\y+z=0\\z+x=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=-y\\y=-z\\z=-x\end{matrix}\right.\)
* x = -y
\(\dfrac{1}{x^{2007}}+\dfrac{1}{y^{2007}}+\dfrac{1}{z^{2007}}=\dfrac{1}{x^{2007}}-\dfrac{1}{x^{2007}}+\dfrac{1}{z^{2007}}=\dfrac{1}{z^{2007}}\)(*)
\(\dfrac{1}{x^{2007}+y^{2007}+z^{2007}}=\dfrac{1}{x^{2007}-x^{2007}+z^{2007}}=\dfrac{1}{z^{2007}}\)(*)
Từ (*) và (**) \(\Rightarrow\) đpcm
Tương tự xét y = -z và z = -x
Vậy nếu x, y, z khác 0 và x + y +z khác 0 thì \(\dfrac{1}{x^{2007}}+\dfrac{1}{y^{2007}}+\dfrac{1}{z^{2007}}=\dfrac{1}{x^{2007}+y^{2007}+z^{2007}}\).
18 tháng 8 2018
giúp mình giải bài này nhanh nhé bởi vì mình hơi bận một chút
17 tháng 4 2021
Giải:
Ta có: N=2019+2020/2020+2021
=>N=2019/2020+2021 + 2020/2020+2021
Vì 2019/2020 > 2019/2020+2021 ; 2020/2021 > 2020/2020+2021
=>M>N
Vậy ...
Chúc bạn học tốt!
17 tháng 4 2021
Ta có : \(\dfrac{2019}{2020}>\dfrac{2019}{2020+2021}\)
\(\dfrac{2020}{2021}>\dfrac{2020}{2020+2021}\)
\(\Rightarrow\dfrac{2019}{2020}+\dfrac{2020}{2021}>\dfrac{2019+2020}{2020+2021}\)
\(\Rightarrow M>N\)
ND
Nguyễn Đức Trí
VIP
1 tháng 12 2023
\(A=\dfrac{2020^{2018}-1}{2020^{2019}+2019}\)
\(B=\dfrac{2020^{2019}+1}{2020^{2020}+2019}\)
Ta có :
\(A-B=\dfrac{2020^{2018}-1}{2020^{2019}+2019}-\dfrac{2020^{2019}+1}{2020^{2020}+2019}\)
\(\Rightarrow A-B=\dfrac{\left(2020^{2018}-1\right)\left(2020^{2020}+2019\right)-\left(2020^{2019}+2019\right)\left(2020^{2019}+1\right)}{\left(2020^{2019}+2019\right)\left(2020^{2020}+2019\right)}\)
\(\Rightarrow A-B=\dfrac{2020^{4038}+2019.2020^{2018}-2020^{2020}-2019-2020^{4038}-2020^{2019}-2019.2020^{2018}-2029}{\left(2020^{2019}+2019\right)\left(2020^{2020}+2019\right)}\)
\(\Rightarrow A-B=\dfrac{-\left(2020^{2020}+2020^{2019}+2.2019\right)}{\left(2020^{2019}+2019\right)\left(2020^{2020}+2019\right)}\)
mà \(\left\{{}\begin{matrix}-\left(2020^{2020}+2020^{2019}+2.2019\right)< 0\\\left(2020^{2019}+2019\right)\left(2020^{2020}+2019\right)>0\end{matrix}\right.\)
\(\Rightarrow A-B< 0\)
\(\Rightarrow A< B\)
Vậy ta được \(A< B\)
\(\dfrac{2020x13+13+2007+2020x2007}{2020x\left(1+520+1500\right)}\)
\(\dfrac{2020x\left(1+13+2007\right)}{2020x\left(1+520+1500\right)}=\dfrac{2021}{2021}=1\)
A = \(\dfrac{2021\times13+2007+2020\times2007}{2020+2020\times520+1500\times2020}\)
A = \(\dfrac{2021\times13+\left(2007+2020\times2007\right)}{2020+2020\times520+1500\times2020}\)
A = \(\dfrac{2021\times13+2007\times\left(1+2020\right)}{2020\times\left(1+520+1500\right)}\)
A = \(\dfrac{2021\times13+2007\times2021}{2020\times2021}\)
A = \(\dfrac{2021\times\left(13+2007\right)}{2021\times2020}\)
A = \(\dfrac{2021\times2020}{2021\times2020}\)
A = 1