fix typo in comment

doc/Language/math.pod6

@@ -308,14 +308,14 @@ To fully understand what is going on, let me explain it step by step.
 First we load the module that make
 the calculations: L<C<Math::Model>|https://github.com/moritz/Math-Model>.
 
-=begin code :skip-test<Snippet for explanantion purposes>
+=begin code :skip-test<Snippet for explanation purposes>
 use Math::Model;
 =end code
 =end item
 
 =begin item
 We create the model to add all the information in it.
-=begin code :skip-test<Snippet for explanantion purposes>
+=begin code :skip-test<Snippet for explanation purposes>
 my $m = Math::Model.new(
 =end code
 =end item
@@ -325,7 +325,7 @@ We declare the derivatives that are in our model. In this case, if
 you remember our equation, we have our variable I<x> and its derivative
 I<x'> (usually know as the velocity).
 
-=begin code :skip-test<Snippet for explanantion purposes>
+=begin code :skip-test<Snippet for explanation purposes>
 derivatives => {
     velocity     => 'x',
     },
@@ -338,7 +338,7 @@ formulas for the derivatives that are not also integration variables
 (in this case, only I<x>), and for other variables we use in the formulas
  (the growth rate).
 
-=begin code :skip-test<Snippet for explanantion purposes>
+=begin code :skip-test<Snippet for explanation purposes>
 variables   => {
     velocity           => { $:growth_constant * $:x},
     growth_constant    => { 1 },   # basal growth rate
@@ -352,7 +352,7 @@ Finally we declare our initial conditions and use I<captures> to
 tell L<C<Math::Model>|https://github.com/moritz/Math-Model> which
 variable or variables to record while the simulation is running.
 
-=begin code :skip-test<Snippet for explanantion purposes>
+=begin code :skip-test<Snippet for explanation purposes>
 initials    => {
     x       => 3,
 },