Every domino covers one black square and one white. Opposite corners are the same colour, so what’s left has 32 squares of one colour and 30 of the other, and 31 dominoes can never cover that.
Cut two diagonally opposite corner squares off a chessboard, leaving 62 squares. Can you cover what’s left exactly with 31 dominoes, each covering two squares side by side?
Give me a hintThe hint
What colour are the two corners you cut off?