Fix details/summary tags

mechanical/mmme1026_maths_for_engineering/calculus.md

@@ -23,7 +23,8 @@ $f(x)$.
 
 </details>
 
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+<details>
+<summary>
 
 ### Rational Functions
 
@@ -31,13 +32,12 @@ A function of the type
 
 $$ \frac{f(x)}{g(x)} $$
 
-<summary>
+</summary>
 
 where $f$ and $g$ are polynomials, is called a rational function.
 
 Its range has to exclude all those values of $x$ where $g(x) = 0$.
 
-</summary>
 </details>
 
 ### Inverse Functions
@@ -85,7 +85,7 @@ If the two limits are equal, we simply refer to the *limit*.
 
 $$f(x) = e^x = \exp x$$
 
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 <summary>
 It can also be written as an infinite series:
 </summary>