$2-$D: Two speakers are placed $5$ m apart. Both play an identical $440$ hz tone at the

same volume, in phase with each other. Assume that the speed of sound in air is

$340$ m$/$s$.$

Find the two points $($locations$)$ closest to the mid$-$point between the speakers at

which a tiny microphone could be placed and perpetually pick up $($detect$,$ measure$)$

nothing but silence.