áp dụng bđt Schwarz thôi mak :

A >/ (x+y+z)/2

phần còn lại là c/m x+y+z >/ căn xy + căn yz + căn zx >/ 1 =>A >/ 1/2

thật lòng xin lỗi anh chị , em mới hok lớp 6 hà !!!!!!

vậy à mình ở bảng B may quá

mik cũng vậy

Vì \(\left(x-2\right)^4\ge0;\left(2y-1\right)^{2004}\ge0\forall x;y\)

\(\Rightarrow\left(x-2\right)^4+\left(2y-1\right)^{2004}\ge0\forall x;y\)

Mà đề lại cho \(\left(x-2\right)^4+\left(2y-1\right)^{2004}\le0\Rightarrow\left(x-2\right)^4=0;\left(2y-1\right)^{2004}=0\)

\(\Rightarrow x=2;y=\frac{1}{2}\) Thay vào đa thức \(21x^{2y}+4xy^2\) ta được :

\(21.2^{2.\frac{1}{2}}+4.2.\left(\frac{1}{2}\right)^2=21.2+8.\frac{1}{4}=42+2=44\)

ban lam j vay

b viết cái gì dợ

là 9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999

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