1. The problem statement, all variables and given/known data Determine the B field at a point P with distance d from centre of current ring radius r (d>r ie outside ring of current) but IN the Plane of ring (i.e off the axis) 2. Relevant equations Biot savart: db=(u.I/4pi.r^2).dl.sinx u=mu, I=current, x=angle made with current vector element dl and vector r connecting P to dl. 3. The attempt at a solution the angle x will vary at all points along ring with vector joining point P, as will r. I will integrate from 0 to 2pi my expression for db but with r^2=a^2+d^2-2adcosy where y is angle between radial vector and d. I am stuck because cannot determine how to express y in terms of x. and thus cannot integrate! many thanks!