calibcant/discussion.tex: Fix simplifying multiplication for eq:peak-frequency

We can divide out all the things that *aren't* zero, and still have
the right hand side be equal to zero.  However, that doesn't mean that
the new right hand side is the same as the old right hand side ;).

diff --git a/src/calibcant/discussion.tex b/src/calibcant/discussion.tex
index 8b0f9e23449e01c53a3ca112c4b1f760db0b5e5f..5f40cc780b8b0ab735987e7ddce44ddd8092a877 100644 (file)
--- a/src/calibcant/discussion.tex
+++ b/src/calibcant/discussion.tex
@@ -51,8 +51,8 @@ frequency of the resonant peak.
   0 &= \deriv{f}{\PSD_f}
     = \frac{2G_{1f}f_\text{max}}
            {\p({(f_0^2-f_\text{max}^2)^2 + \beta_f^2 f_\text{max}^2})^2}
-      \p({2(f_0^2-f_\text{max}^2) - \beta_f^2})
-    = 2(f_0^2-f_\text{max}^2) - \beta_f^2 \\
+      \p({2(f_0^2-f_\text{max}^2) - \beta_f^2}) \\
+    &= 2(f_0^2-f_\text{max}^2) - \beta_f^2 \\
   f_\text{max}^2 &= f_0^2 - \frac{\beta_f^2}{2} \\
   f_\text{max} &= \sqrt{f_0^2 - \frac{\beta_f^2}{2}} \;,
   \label{eq:peak-frequency}