# [Maxima] Solving Equations With logs

Marco Carmosino mogunus at gmail.com
Mon Feb 18 11:12:03 CST 2008

```Hello all. I am trying to find all points where two functions intersect,
using maxima.

These are my function definitions:

(%i29) log2(x) := log(x)/log(2)
(%i84) eq1 : y = 64*n*log2(n)\$
(%i85) eq2 : y = 8*n^2\$

When I use:

solve([eq2,eq1],[n,y]);

I get:

`algsys' cannot solve - system too complicated.
-- an error.  To debug this try debugmode(true);

I've tried using "pickapart" at levels 1, 2, and 3 on eq1, but I still get
the same error message when I execute:

solve([eq2,%],[n,y]);

When I use find_root, with the same equation definitions, I get two
different replies depending on whether I pick y or n as my variable:

(%i99) find_root([eq2,eq1],y,1,100);
Is  n  positive or negative?

positive;
Is  n  positive or negative?

positive;
2      64 n log(n)
(%o99)       find_root([y = 8 n , y = -----------], y, 1.0, 100.0)
log(2)

I think I am responding to the "positive or negative" prompt wrong, but I
couldn't find how to respond properly in the docs.

(%i96) find_root([eq2,eq1],n,1,100);
2      64 n log(n)
(%o96)       find_root([y = 8 n , y = -----------], n, 1.0, 100.0)
log(2)

Sorry about the length of this, but I wanted to specify exactly what I
tried. Thanks very much for any help.

--Marco
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