Elementary Mathematics Dorofeev < 2027 >

Why? Color the 5×5 board in a clever way — not like a chessboard (alternating black-white), but in three colors repeating diagonally:

But our shape after removing a corner has: Color 0: 9 Color 1: 8 Color 2: 7 elementary mathematics dorofeev

Thus, . 5. The Contradiction If 8 trominoes tile the shape, they would cover: 8 trominoes × 1 square of each color = 8 of Color 0, 8 of Color 1, 8 of Color 2. 8 of Color 1