Fixes text and examples

I fact, it was more wrong than indicated for the OP. Thanks for
drawing our attention to this. Closes #2482

doc/Type/Cool.pod6

@@ -272,16 +272,17 @@ radians.
 
 Defined as:
 
-    sub atan2(Numeric() $x, Numeric() $y = 1e0)
     method atan2($y = 1e0)
 
-Coerces the arguments (including the invocant in the method form) to
-L<Numeric|/type/Numeric>, and returns their two-argument
-L<arc-tangent|https://en.wikipedia.org/wiki/Inverse_trigonometric_functions> in
-radians.
+Coerces self and argument to L<Numeric|/type/Numeric>, using them to compute the
+two-argument L<arc-tangent|https://en.wikipedia.org/wiki/Atan2> in radians.
 
-    say atan2(3);               # OUTPUT: «1.24904577239825␤»
     say 3.atan2;                # OUTPUT: «1.24904577239825␤»
+    say ⅔.atan2(⅓);             # OUTPUT: «1.1071487177940904␤»
+
+The first argument defaults to 1, so in the first case the function will return
+the angle θ in radians between a vector that goes from origin to the point (3,1)
+and the x axis.
 
 =head2 routine sec