why electric field in equitorial dipole -ve???

The direction of an electric dipole is along the length of the dipole and is directed from the negative charge towards the positive charge. In the equatorial plane, the electric field at any point is perpendicular to the equatorial plane (or parallel to the length of the dipole). The electric field lines are as shown in the diagram has a direction opposite to that of the direction of the dipole.

So, the electric field at the equatorial plane of the dipole is negative.