Review of lines in the plane and their equations. Intersections of lines in the plane. Best-fit lines in the plane via the method of least squares (linear regression). Systems of linear equations. Gaussian and Gauss-Jordan elimination. Underdetermined and overdetermined systems. The method of least squares again. Matrices, linear transformations, and elementary row operations. Computer implementation. Matrix algebra. Systems of linear inequalities and linear programming. Best-fit lines via the method of least absolute deviations. Computer implementation.