Hello David,
thank you answering my question.
Now I changend the code, using a variable:
(%i2) eq10: w1-w2=-a*(p-d-m)^2+a*(p-m)^2;
(%i3) eq11: w3-w2=-s*(p+d-m)^2+s*(p-m)^2;
(%i4) q: solve(eq10,[a]);
(%i5) eq12: subst(q,s,eq11);
now here I get the result I wanted to have.
Finally, I was interested in m, with no dependencies to a or s.
So, I wanted to have
m= expression. In order to get this, I commanded:
(%i6) solve(eq12,[m]);
Instead, I get no calculation result...
Thanks in advance
ERik