\(x=\sqrt{7+4\sqrt{3}}\)

\(x=\sqrt{4+4\sqrt{3}+3}\)

\(x=\sqrt{\left(2+\sqrt{3}\right)^2}\)

\(x=2+\sqrt{3}\)

Ta có ;

A=\(\sqrt{3}-\sqrt{x^2-4x+4}\)

A=\(\sqrt{3}-\sqrt{\left(x-2\right)^2}\)

Thay x vào A ta có 

A=\(\sqrt{3}-\sqrt{\left(2+\sqrt{3}-2\right)^2}\)

A=\(\sqrt{3}-\sqrt{\left(\sqrt{3}\right)^2}\)

A=\(\sqrt{3}-\sqrt{3}\)

A=0

Vậy A=0 <=>x=\(\sqrt{7+4\sqrt{3}}\)

^{_{\(\dfrac{11}{8}+\dfrac{13}{6}=\dfrac{85}{x}\)}}

\(\dfrac{33}{24}+\dfrac{52}{24}=\dfrac{85}{x}\)

^{_{\(\dfrac{85}{24}=\dfrac{85}{x}\)}}

x=24

CD là 360:9=40

CV HCN là (40+9)x2=98

Vậy CV HCN là 98cm