In mathematics it is often convenient to consider square or rectangular arrays of numbers in what is known as a matrix, (matrices is the plural). One of the changes in Project Maths was to remove a study of matrices from the Leaving Cert syllabus.
But if you continue on to third level courses you are still likely to encounter these very useful arrangements. For example, they may be used to solve a system of linear equations. I have just come across a very nice little matrix calculator on one of my favourite maths websites. It can be accessed at www.mathsisfun.com/algebra/matrix-calculator.html or via my page “Simple Graphing and other Calcultors” under the “Resources” tag.