Correct Answer - `(mu_0)/(2pia)(I_1^2+I_2^2)^(1//2)`
Magnetic field induction at P due to current through AOB and COD will be
`B_1=(mu_0)/(4pi)(2I_1)/(a)` and `B_2=(mu_0)/(4pi)(2I_2)/(a)`
Here `vecB_1` and `vecB_2` are perpendicular to each other.
The magnitude of resultant magnetic field induction will be
`B=sqrt(B_1^2+B_2^2)=[((mu_0)/(4pi)(2I_1)/(a))^2+((mu_0)/(4pi)(2I_2)/(a))^2]^(1//2)`
`=(mu_0)/(2pia)(I_1^2+I_2^2)^(1//2)`