\(A=\left(y-2\text{x}-1\right)^2+\left(3-x\right)^2-4y+2019\)
A=\(y^2+4\text{x}^2+1-4\text{x}y+4\text{x}-2y+9-6\text{x}+x^2-4y+2019\)
A=\(y^2-6y+5\text{x}^2-2\text{x}-4\text{x}y+2029\)
A=\(y^2-2y\left(2\text{x}+3\right)+\left(2\text{x}+3\right)^2-\left(2\text{x}+3\right)^2+5\text{x}^2-2\text{x}+2029\)
A=\(\text{[}y-\left(2\text{x}+3\right)\text{]}^2-\left(4\text{x}^2+12\text{x}+9\right)+5\text{x}^2-2\text{x}+2029\)
A=\(\text{[}y^2-\left(2\text{x}+3\right)\text{]}^2+x^2-14\text{x}+49+1971\)
A=\(\text{[}y^2-\left(2\text{x}+3\right)\text{]}^2+\left(x-7\right)^2+1971\)
vì \(\text{[}y-\left(2\text{x}+3\right)\text{]}^2\ge0\) với mọi x,y thuộc R
\(\left(x-7\right)^2\ge0\) với mọi x thuộc R
1971>0
vậy MIN A=1971 đạt tại x=7\(\Rightarrow\) y=17
like giúp mình để có động lực nha
