Answer 1

Ta có:

\(\left(3AC\right)^2=AC^2+4\)

\(\Leftrightarrow9AC^2=AC^2+4\)

\(\Leftrightarrow8AC^2=4\)

\(\Leftrightarrow AC^2=\dfrac{1}{2}\)

Answer 2

\(\left(3AC\right)^2=AC^2+4\)

\(\Rightarrow9AC^2=AC^2+4\)

\(\Rightarrow9AC^2-AC^2=4\)

\(\Rightarrow8AC^2=4\)

\(\Rightarrow AC^2=\dfrac{4}{8}=\dfrac{1}{2}\)