A Hidden Triple is three cells that are part of the same group and contain the same three candidates which are not present in any other cells in the group. The three hidden triple cells should contain more than the three candidates. This means that we can remove all other candidates from the Hidden Triple cells other than the hidden candidates.
If the hidden tripple candidates only appear three or two times in the group and only in these three cells, they must be the solutions for the cells. Therefore all other candidates in the three hidden triple cells can be elliminated.
All 3 candidate do not have to appear in all 3 cells, but they must not appear in any other cells and they must not form a hidden pair. If A, B and C are the candidate values, the following combination of values in the cells are possible:
[(ABC),(ABC),(ABC)], [(ABC),(ABC),(AB)], [(ABC),(ABC),(AC)], [(ABC),(ABC),(BC)], [(ABC),(AB),(BC)], [(ABC),(AC),(AB)], [(ABC),(AC),(BC)], [(AB),(AC),(BC)]
3, 6 and 8 form the hidden triple in Box 3.
3, 4 and 6 form the hidden triple in Row 7.
1, 2 and 3 form the hidden triple in Column 7.
If you tap on the following links on an iOS device which has the Sudoku Tutor app installed, it will launch the app and open the practice puzzle. Tap hint once the puzzle is open to see the strategy in action.Sample Puzzle 1 Sample Puzzle 2 Sample Puzzle 3