\(B_1=2.10^{-7}.\dfrac{I_1}{r^2}\left(T\right)\)
\(B_2=2.10^{-7}.\dfrac{I_2}{\left(r+0,7\right)^2}\left(T\right)\)
\(B_1=B_2\Leftrightarrow\dfrac{I_2}{\left(r+0,7\right)^2}=\dfrac{I_1}{r^2}\)
\(\Leftrightarrow\dfrac{2\sqrt{3}}{r+0,7}=\dfrac{2\sqrt{2}}{r}\Leftrightarrow2\sqrt{3}r-2\sqrt{2}r=0,7.2\sqrt{2}\Rightarrow r=...\left(m\right)\)