your calculator is not able to handle symbols like . It has a build-in function which returns an approximative value. For instance: If you type the calculator uses 3.872983346.. and as far as I'm informed the TI84 uses internally(?) 14 decimals and rounds a result down to maximal 12 decimals.
So considering the abilities of your calculator all results are OK.
If you take #1:
This method is called calculating a root partially: A value is transformed into a product of a square and a non-square(?). You can calculate the square-root of the square. But your calculator isn't able to do these transformations.