anh đi anh nhớ quê nha 

nhớ canh rau muống nhớ cà dầm tương 

nhớ thằng đẩy bố xuống mương 

bố mà bắt được bố tương vỡ mồm

ko phai bang 4 dau minh thi r ma!

Tham khảo

\(A=\left(b+a\right)+\left(c-d\right)-\left(c+a\right)-\left(b-d\right)\)

\(A=b+a+c-d-c-a-b+d\)

\(A=\left(b-b\right)+\left(a-a\right)+\left(c-c\right)+\left(-d+d\right)\)

\(A=0\)

\(B=\left(a-d\right)-\left(d+a\right)-\left(c-d\right)+\left(c+b\right)\)

\(B=a-d-d-a-c+d+c+b\)

\(B=\left(a-a\right)+\left(d-d+d\right)+\left(-c+c\right)+b\)

\(B=d+b\)

a) Ta có: \(A=\left(b+a\right)+\left(c-d\right)-\left(c+a\right)-\left(b-d\right)\)

\(=a+b+c-d-c-a-b+d\)

=0

b) Ta có: \(B=\left(a-d\right)-\left(a+d\right)-\left(c-d\right)+\left(c+b\right)\)

\(=a-d-a-d-c+d+c+b\)

=b-d

Ta có : \(\frac{a}{b}=\frac{b}{c}=\frac{c}{d}=\frac{d}{a}=\frac{a+b+c+d}{b+c+d+a}=1\Rightarrow a=b=c=d\)

Khi đó P = \(\frac{2019a-b}{c+d}+\frac{2019b-c}{d+a}+\frac{2019c-d}{a+b}+\frac{2019d-a}{b+c}\)

\(=\frac{2019a-a}{2a}+\frac{2019b-b}{2b}+\frac{2019c-c}{2c}+\frac{2019d-d}{2d}\)

\(=1014+1014+1014+1014=1014.4=4056\)

Áp dụng t/c dttsbn:

\(\dfrac{a+b+c-2020d}{d}=\dfrac{b+c+d-2020a}{a}=\dfrac{c+d+a-2020b}{b}=\dfrac{d+a+b-2020c}{c}=\dfrac{3\left(a+b+c+d\right)-2020\left(a+b+c+d\right)}{a+b+c+d}=-2017\)

\(\Rightarrow\left\{{}\begin{matrix}a+b+c-2020d=-2017d\\b+c+d-2020a=-2017a\\c+d+a-2020b=-2017b\\d+a+b-2020c=-2017c\end{matrix}\right.\\ \Rightarrow\left\{{}\begin{matrix}a+b+c=3d\\b+c+d=3a\\c+d+a=3b\\d+a+b=3c\end{matrix}\right.\Rightarrow a=b=c=d\)

\(F=\dfrac{a+b}{c+d}+\dfrac{b+c}{d+a}+\dfrac{c+d}{a+b}+\dfrac{a+d}{b+c}\\ F=\dfrac{a+a}{a+a}+\dfrac{a+a}{a+a}+\dfrac{a+a}{a+a}+\dfrac{a+a}{a+a}=4\)