Published on by JGD
# HP Prime - equation systems basics

Let’s see: linear equation systems. My elder child is now beginning with equations. They don’t use calculators at school so far, relying in good old blackboard learning. Of course, they are starting with 2 equations with 2 unknowns.

I have thought to myself that I should give him a couple of calculators - a HP Prime so that he can learn maths in depth; and a HP15c (that I am keeping for him anew) so that he can use it in class as a normal calculator - while it is a complete workhorse that will allow him to do matrix work - even if graphical calculators are forbidden.

I showed to him how to use the linear solver app in the Prime. You can use it for 2x2 and 3x3 equation system, and the app solves it to you, tells you if there is solution, if there are infinite solutions or if there cannot be a solution.

But then he asked me what would happen, should there be 4x4 systems or greater. I replied to him “don’t worry, there is a tool for that: matrixes”.

But then, I asked to myself, how to use matrixes to solve equation systems? I mean, would it be necessary to follow the rule: invert the coefficient matrix, and then “pre-multiply” the constants vector by it?

[X]=[A]–1x[C]

I know this should work - but what I meant, was the HP15c way: take the [C] vector to the stack, take the [A] matrix to the stack, and then divide (the usual divide key). Hardly the syntactically correct way, but it is the intuitive way (and a shortcut that worked in the HP15c)

Well, it also works the “shortcut” way!

And while you can write matrixes on the command line, I would always recommend to use the Matrix Editor.

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