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When I run the 3x3 linear equations solver, it opens me the window where I can solve two linear equations only. The 3rd linear equation is missing. How can I fix it?

To solve 3x3 systems, you need to rotate your device to landscape orientation. In landscape orientation, you can solve both 2x2 and 3x3 systems.

In portrait orientation, you can solve 2x2 systems only.