@Kitonum 

Exactly! I didn't know the word for it in English. But yes, basically.

And I was wondering if a command could do it for me :)

@Kitonum 

So the expression should be simplified first?

It looks great though, thanks!

EDIT:

Even if it doesn't give the exact output I'd like. Either way, nice to know it can be done this way.

@Axel Vogt 

Ah, sorry!

The image shows this:

> k:=student[completesquare](%=0,[x1,y1]); 

k:=25(y1-5)^2-100+100*x1^2=0

> k+100: %/25: %/100;

1/100(y1-5)^2+1/25*x1^2=1/25

> %*25

1/4(y1-5)^2+x1^2=1

@Axel Vogt 

I'd like to see the expression for an ellipse but I'm starting to think it's too much work..

After all the result can be acomplished with a few lines. I was just wondering if it was possible.

In short I'd like a commando to do this for me:

@acer 

Ah, it makes a lot of sense. Thanks again :)

Lign5 is just a "fresh" function we were told to substitute into the matrix. This is all for a school assignment.

@acer 

Thanks a lot for your very helpful answer :)

Even if it's kind of annoying that a simple "subs" won't do the trick.