I have two equations as below:

eq1: $8 \pi \gamma r-\frac{4 \pi \text{Delta$\_\mu $} r^2}{\text{v$\_$c}}=0$

eq2: $\text{Delta$\_\mu $}=\text{K$\_$b} S T$

When I try Solve[{eq1}, {r}], I obtained $\left\{\{r\to 0\},\left\{r\to \frac{2 \gamma \text{v$\_$c}}{\text{Delta$\_\mu $}}\right\}\right\}$.

This is correct, but I want it is expressed as $\left\{r\to \frac{2 \gamma \text{v$\_$c}}{\text{K$\_$b} S T}\right\}$. I tried Solve[{eq1, eq2}, {r}] but I obtained {}

How can I get the result expressed with K_b, S and T instead of Delta_u? Many thanks!

  • 5
    $\begingroup$ it is better to post the actual Mathematica plain source code you used. Also _ can't be used in variable names. $\endgroup$ – Nasser Dec 21 '15 at 11:03
  • 1
    $\begingroup$ Try Eliminate. $\endgroup$ – Sjoerd C. de Vries Dec 21 '15 at 11:11
  • $\begingroup$ Or Solve for both Delta_u and r (I trust the actual "variable" does not have an underbar in it). $\endgroup$ – Daniel Lichtblau Dec 21 '15 at 16:10
Format[v[c]] := Subscript[v, c];
Format[K[b]] := Subscript[K, b];
Format[Delta[u]] := Subscript[Delta, u];

Solve[8 π γ r - 4 π Delta[u] r^2/v[c] == 0, r] /. 
 Delta[u] -> K[b] S T

enter image description here

  • $\begingroup$ Thanks! This is exactly what I want. Sorry that I cannot vote for your answer since I do not have sufficient reputation. $\endgroup$ – user2230101 Dec 22 '15 at 6:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.