\(A=\sqrt{\left(\dfrac{1}{2}-x\right)^2+\left(\dfrac{\sqrt{11}}{2}\right)^2}+\sqrt{\left(\dfrac{1}{2}+x\right)^2+\left(\dfrac{\sqrt{11}}{2}\right)^2}\)
\(\ge\sqrt{\left(\dfrac{1}{2}-x+\dfrac{1}{2}+x\right)^2+\left(\dfrac{\sqrt{11}}{2}+\dfrac{\sqrt{11}}{2}\right)^2}\)
\(=\sqrt{12}\)
"=" xảy ra khi x = 0