Typo fix.

07-Kalman-Filter-Math.ipynb

@@ -523,7 +523,7 @@
     "\n",
     "For the Kalman filter we will be using a form of the series that uses a matrix. But before we do that, let's work through a couple of examples with real functions since real functions are easier to plot and reason about. The Taylor series for either are nearly identical, so this is a good first step.\n",
     "\n",
-    "For a real or complex function the Taylor series of a function $f(x)$ evaluated at $a$ is defined as \n",
+    "For a real or complex function the Taylor series of a function $f(x)$ evaluated at $t$ is defined as \n",
     "\n",
     "$$ \\Phi(t) = e^{\\mathbf{F}t} = \\mathbf{I} + \\mathbf{F}t  + \\frac{(\\mathbf{F}t)^2}{2!} + \\frac{(\\mathbf{F}t)^3}{3!} + ... $$\n",
     "\n",