Hello and welcome to this course on the hidden pair technique!
This technique is very simple to understand, but you will have to be careful to detect hidden pairs.
The Hidden Pair Technique
If there are two cells in a house where there are two candidates who do not appear anywhere outside of those cells in the same house, those candidates must be placed in both cells.
All other candidates can then be eliminated from those two cells.
Let's look closely at column C5.
Cells R2-C5 and R7-C5 are the only cells that have 2 and 5 as candidates.
Therefore, it is safe to delete the other candidates in these cells.