${\text { Resultant field, } B=\sqrt{B_{1}^{2}+B_{2}^{2}}}$
${\text { But } B_{1}=\frac{\mu_{0} I_{1}}{2 \pi d} \text { and } B_{2}=\frac{\mu_{0} I_{2}}{2 \pi d}}$
${\therefore B=\sqrt{\left(\frac{\mu_{0}}{2 \pi d}\right)^{2}\left(I_{1}^{2}+I_{2}^{2}\right)}}$
$or, B=\frac{\mu_{0}}{2 \pi d}\left(I_{1}^{2}+I_{2}^{2}\right)^{1 / 2}$


