If ${N_a} = \{ an : n \in N \}$,then ${N_3} \cap {N_4} = $

Which one of the following statements is not correct?

$A$ coil of radius '$r$' is placed on another coil (whose radius is '$R$' and current through it is changing) so that their centers coincide. $(R \gg r)$. If both are coplanar,then the mutual inductance between them is proportional to

The differential equation of the family of parabolas with vertex at $(0, -1)$ and having axis along the $Y$-axis is

In the circuit shown in the figure,neglecting source resistance,the voltmeter and ammeter readings will respectively be:

An integrating factor of the equation $(1+y+x^2 y) dx+(x+x^3) dy=0$ is