There might be 2 common answers:
- you aren't using the evaluate operator = or CTRL+. or from the buttons in the Arithmetic toolbox:
![2017-10-25 23_49_01-SMath Studio - [Page1].png](/ru-RU/file/mZVQr6/2017-10-25-23_49_01-SMath-Studio---_Page1__png)
- you are using the subscript symbol (decimal symbol) instead of the element function available with [ or el( or from the buttons in the Matrices toolbox:
![2017-10-25 23_54_30-SMath Studio - [Page1].png](/ru-RU/file/hpnQ8r/2017-10-25-23_54_30-SMath-Studio---_Page1__png)
for what I can see from your screenshot, my guess is that you are in the 2nd case

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