dvec$(B)=\frac{{}_{0}r}{4}\frac{\text{d}\text{v}\text{e}\text{c}(k{)}_x(hat(r))}{r^2}$

When using the equationd vec$(B)=\frac{{}_0(d_2^{})*x^{**}}{4r^2}$ to find the magnetic field due to a current in a wire, it is important to recognize that

A$)$ this expression must be integrated over all values of r to find the total magnetic field.

B$)$ this expression must be integrated over the length of the wire to find the total magnetic field.

C$)$ vec$(r)$ is a vector directed from the point at which the field is to be found toward a small element of length vec$(dl)$ on the wire.

D$)$ dvec$(B)$ is the change in magnetic field when one moves an additional distance vec$(dr)$ from the wire.

E$)$ vec$(dl)$ is a small element of displacement along an imaginary path surrounding the wire.