HP Forums

Hello everyone!
How can I solve systems of equations on the HP Prime, i.e., what should I do to get x=-1 and y=11 from the system below:

3x+y=8
x+2y=21

Edit:
Add both equations on the Solve app and solve both ate the same time.

Hi,

There is a nifty App called "Linear Solver" that works great on systems of 2 or 3 equations. For anything greater, there are a couple of ways, but perhaps the easiest way is the use the RREF() command, taking a 2x3 matrix of the coefficients.

Good luck and take care,

Steve

One way:
[CAS]
solve({(3*x+y) = 8,(x+2*y) = 21},{x,y})

Another way:
[CAS]
col(RREF([[3,1,8],[1,2,21]]),3)

Hello,
there is an app for small systems of linear equations (2 unknowns in 2 equations and 3 unknowns in 3 equations). You find it by pressing Apps and tapping on Linear Solver.
Hope that helps
Thomas

My favorite way to solve linear systems is an efficient way on the keyboard: just a single division. The example below is the system you gave above. The screen capture on the left is with Textbook Display Mode turned on, and the one on the right is with it turned off, otherwise they are identical.



This nifty method works with any size system. Just be sure to use single square bracket for the numerator (which contains the constants from the right side of the equations) and double square brackets for the denominator (which contains the coefficients from the left side of the equations). If your Prime flashes a warning at you, saying something like "This shortcut is a Bad Thing which we included only under pressure from users of previous HP calculator models", ignore it.

Thanks for all the help guys!

One more thing: how can I do a inequalities system?

I'm trying to solve this one and I did not manage to do so:

y ≤ 3x+1
x-y > 1

I think the Advanced Graphing app handles inequalities nicely. A couple of things to notice though:

1. Separate implicit multiplications: y ≤ 3x+1 should be: Y ≤ 3*X+1, etc.
2. Using the apps requires UPPER case variables!
y ≤ 3x+1 ==> Y ≤ 3*X+1

Enter your equations with those two changes into the Advanced Graphing app [Symb] page, and then use the [Plot] page to view your results.