Question

find electric potential due to dipole at its axial point opposite to direction of dipole moment​

Answer 1

The NCERT formula is correct if used with vector notation as the direction of electric dipole moment is from -q(negative charge) to +q(positive charge) and the resultant electric field at any point on equatorial line is in direction opposite to the electric dipole moment so negative sign is used. The other formula which does not include negative sign is applicable to calculate the magnitude(not direction) of electric field.

hope this answer helpful u