What is Hidden Pair? How to Solve Sudoku

What it is

If, in a row (column or box), both 2 and 6 can only go in the same two cells, those two cells must be 2 and 6.

So you can remove every other candidate from those two cells.

Unlike a Naked Pair, the cells may show lots of candidates — but 2 and 6 have nowhere else to go.

In a group, look for a digit with only two possible spots, then check whether another digit has exactly the same two spots.

Yellow cells are where to look, orange cells are the reason, red digits are candidates you can remove, and the blue digit is the answer.

In box 8, both 4 and 8 can only go in R7C5 and R8C5. Those two cells must be 4 and 8, so remove their other candidates (7 and 9).