Updates the return values to reflect what the product actually returns. (#754)

From
[CIP-49](https://docs.google.com/document/d/1PHnAYYAe9U97YtKpZyaMObhhjEferE_Ynw5gYhRiXTs/edit#heading=h.lzdax825k5wi)

---------

Author: gem-neo4j

modules/ROOT/pages/functions/mathematical-logarithmic.adoc

@@ -87,6 +87,7 @@ e(expression)
 |===
 
 | `exp(null)` returns `null`.
+| `exp()` returns `Infinity` when the return value is greater than the largest `FLOAT` value (Java Double.MAX_VALUE).
 
 |===
 
@@ -150,7 +151,8 @@ log(expression)
 |===
 
 | `log(null)` returns `null`.
-| `log(0)` returns `null`.
+| `log(0)` returns `-Infinity`.
+| If (`expression` < 0), then (`log(expression)`) returns `NaN`.
 
 |===
 
@@ -215,7 +217,8 @@ log10(expression)
 |===
 
 | `log10(null)` returns `null`.
-| `log10(0)` returns `null`.
+| `log10(0)` returns `-Infinity`.
+| If (`expression` < 0), then (`log10(expression)`) returns `NaN`.
 
 |===
 
@@ -280,7 +283,7 @@ sqrt(expression)
 |===
 
 | `sqrt(null)` returns `null`.
-| `sqrt(<any negative number>)` returns `NaN`
+| If (`expression` < 0), then (`sqrt(expression)`) returns `NaN`.
 
 |===
 

modules/ROOT/pages/functions/mathematical-trigonometric.adoc

@@ -40,7 +40,7 @@ acos(expression)
 |===
 
 | `acos(null)` returns `null`.
-| If (`expression` < -1) or (`expression` > 1), then (`acos(expression)`) returns `null`.
+| If (`expression` < -1) or (`expression` > 1), then (`acos(expression)`) returns `NaN`.
 
 |===
 
@@ -102,7 +102,7 @@ asin(expression)
 |===
 
 | `asin(null)` returns `null`.
-| If (`expression` < -1) or (`expression` > 1), then (`asin(expression)`) returns `null`.
+| If (`expression` < -1) or (`expression` > 1), then (`asin(expression)`) returns `NaN`.
 
 |===
 
@@ -359,7 +359,7 @@ cot(expression)
 |===
 
 | `cot(null)` returns `null`.
-| `cot(0)` returns `null`.
+| `cot(0)` returns `Infinity`.
 
 |===