#!/bin/bash
s='Mon0 connected 1920x1200+0+0 0mm x 0 mm
   1920x1200_c 59.95*
Mon0 connected 1920x1200+0+0 0mm x 0 mm
   1920x1200_c 59.95*
Mon0 connected primary 1920x1200+0+1200 0mm x 0 mm
   1920x1200_c 59.95*
Mon0 connected 1029x1200+1920+1200 0mm x 0 mm
   1920x1200_c 59.95*'

echo "$s" | grep -oP '\b\d+x\d+(?!(?:\+\d+\+)?\d)'