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Ta có : \(P=\frac{a}{b+c}+\frac{b}{c+a}+\frac{c}{a+b}\)
\(\Rightarrow P+3=\frac{a}{b+c}+1+\frac{b}{c+a}+1+\frac{c}{a+b}+1\)
\(\Rightarrow P+3=\frac{a+b+c}{b+c}+\frac{a+b+c}{c+a}+\frac{a+b+c}{a+b}\)
\(\Rightarrow P+3=\left(a+b+c\right).\frac{1}{b+c}+\left(a+b+c\right).\frac{1}{c+a}+\left(a+b+c\right).\frac{1}{a+b}\)
\(\Rightarrow P+3=\left(a+b+c\right).\left(\frac{1}{b+c}+\frac{1}{c+a}+\frac{1}{a+b}\right)\)
\(\Rightarrow P+3=2019.10\)
\(\Rightarrow P+3=20190\)
\(\Rightarrow P=20190-3\)
\(\Rightarrow P=20187\)
Vậy P = 20187
Ta có :
Đặt \(\frac{a}{2019}\)= \(\frac{b}{2020}\)= \(\frac{c}{2021}\)= k
=> a = 2019k; b = 2020k; c = 2021k
M = 4(a-b).(b-c) - (c-a)
M = 4(2019k- 2020k). (2020k-2021k) - (2021k - 2019k)
M = 4.(-1)k.(-1)k - 2k
M = 4k2 - 2k
(Hình như mình thấy đề bạn có gì sai sai)
Đặt \(\frac{a}{2018}=\frac{b}{2019}=\frac{c}{2020}=k\Rightarrow\hept{\begin{cases}a=2018k\\b=2019k\\c=2020k\end{cases}}\)
Khi đó 4(a - b)(b - c) = 4(2018k - 2019k)(2019k - 2020k)
= 4(-k).(-k)
= 4k2 (1)
Lại có (c - a)2 = (2020k - 2018k)2 = (2k)2 = 4k2 (2)
Từ (1)(2) => 4(a - b)(b - c) = (c - a)2
a) Ta có : \(\frac{-60}{12}=-5=-\frac{25}{5}\)
\(-0,8=-\frac{8}{10}=-\frac{4}{5}\)
Mà -25 < -4 nên \(\frac{-25}{5}< \frac{-4}{5}\)=> \(\frac{-60}{12}< -0,8\)
b) Ta có : \(\frac{2020}{2019}=1+\frac{1}{2019}\)
\(\frac{2021}{2020}=1+\frac{1}{2020}\)
Vì \(\frac{1}{2019}>\frac{1}{2020}\)nên \(\frac{2020}{2019}>\frac{2021}{2020}\)
c) \(\frac{10^{2018}+1}{10^{2019}+1}=\frac{10\left(10^{2018}+1\right)}{10^{2019}+1}=\frac{10^{2019}+10}{10^{2019}+1}=\frac{10^{2019}+1+9}{10^{2019}+1}=1+\frac{9}{10^{2019}+1}\)(1)
\(\frac{10^{2019}+1}{10^{2020}+1}=\frac{10\left(10^{2019}+1\right)}{10^{2020}+1}=\frac{10^{2020}+10}{10^{2020}+1}=\frac{10^{2020}+1+9}{10^{2020}+1}=1+\frac{9}{10^{2020}+1}\)(2)
Đến đây tự so sánh rồi nhé
Đặt \(\frac{a}{2018}=\frac{b}{2019}=\frac{c}{2020}=k\)
\(\Rightarrow a=2018k\), \(b=2019k\), \(c=2020k\)
Ta có: \(4\left(a-b\right)\left(b-c\right)=4\left(2018k-2019k\right)\left(2019k-2020k\right)\)
\(=4.\left(-k\right).\left(-k\right)=4k^2=\left(2k\right)^2\)
Ta lại có: \(\left(a-c\right)^2=\left(2018k-2020k\right)^2=\left(-2k\right)^2=\left(2k\right)^2\)
Vậy \(4\left(a-b\right)\left(b-c\right)=\left(a-c\right)^2\)
Đặt \(\frac{a}{2018}=\frac{b}{2019}=\frac{c}{2020}=k\Rightarrow\hept{\begin{cases}a=2018k\\b=2019k\\c=2020k\end{cases}}\)
Thế vị trí tương ứng ta được :
VT = 4( a - b )( b - c )
= 4( 2018k - 2019k )( 2019k - 2020k )
= 4(-k)(-k)
= 4k2
VP = ( a - c )2
= ( 2018k - 2020k )2
= ( -2k )2
= 4k2
=> VT = VP
=> đpcm
Áp dụng dãy tỉ số bằng nhau ta có:
: \(\frac{a}{2019}\)=\(\frac{b}{2020}\)=\(\frac{c}{2021}=\frac{c-a}{2021-1009}=\frac{a-b}{2019-2020}=\frac{b-c}{2020-2021}\)
=> \(\frac{c-b}{2}=\frac{a-b}{-1}=\frac{b-c}{-1}\)
=> \(\frac{\left(c-b\right)^2}{4}=\frac{\left(a-b\right)\left(b-c\right)}{1}\)
=> \(\left(c-a\right)^2=4\left(a-b\right)\left(b-c\right)\)
Đặt \(\frac{a}{2019}=\frac{b}{2020}=\frac{c}{2021}=y\)
\(\Rightarrow a=2019y;b=2020y;c=2021y\)
\(\Rightarrow\hept{\begin{cases}4\left(a-b\right)\left(b-c\right)=4\left(2019y-2020y\right)\left(2020y-2021y\right)=4\left(-y\right)\left(-y\right)=4y^2\\\left(c-a\right)^2=\left(2021y-2019y\right)^2=4y^2\end{cases}}\)
\(\Rightarrow4\left(a-b\right)\left(b-c\right)=\left(c-a\right)^2\)( ĐPCM )