Question

Is the set B = {$x$ : $x^2+4=0$ and $xϵN$} an empty set?

Find the number of elements for the set B.

Answer 1

The given function $x^2+4=0$ cannot be satisfied by any natural number as the L.H.S is always positive while the R.H.S is zero.

Thus the given set $B$ is an empty set.

Also, the number of elements in it is $0$.