Two short magnetic dipoles N→1=Mi^ and N2⇀=Mj^ are placed at the origin. Then magnetic induction at the point r,0 is
μ04π3Mr3
μ04π2Mr3
μ04π5Mr3
μ04πNr3
B→1=μ04π2Mr3i^
B→2=−μ04πMr3j^
∴ B=B12+B22=μ04π5Mr3