The purpose of this research is to develop a mobile-based application product using the Gauss Jordan method on a valid, effective, and practical system of linear equations. This research is an R&D (Research and Development) research using ADDIE as its development model. Data collection techniques used are material validation sheets and application display; practicality sheet; test sheets (pretest and posttest); and student opinion sheet. The application design technique used is to use mobile programming with Android Studio to design software applications. Based on the data that has been obtained and processed, the average score of the material validation assessment is 4.31 and for media display validation is 4.33, where both these values ​​are included in the valid category, the score for improving student learning outcomes is 0.71 which includes classification. Improvement is high and includes effective, as well as an average score of 4.2 practicality assessment which is included in the high category. The application of this application also received a positive response from students who have used it, so the Gauss Jordan 3x3 application is suitable for use in learning and determining solutions to linear equations.

Keywords: ADDIE; Gauss-Jordan; Linear Equation