Optimize math expression text (#1898)

Co-authored-by: George Peter Banyard <girgias@php.net>

reference/math/functions/acos.xml

@@ -15,7 +15,7 @@
    Returns the arc cosine of <parameter>num</parameter> in radians.
    <function>acos</function> is the inverse function of
    <function>cos</function>, which means that
-   <literal>a==cos(acos(a))</literal> for every value of a that is within
+   <code>$num == cos(acos($num))</code> for every value of a that is within
    <function>acos</function>' range.
   </para>
  </refsect1>

reference/math/functions/asin.xml

@@ -15,7 +15,7 @@
    Returns the arc sine of <parameter>num</parameter> in radians.
    <function>asin</function> is the inverse function of
    <function>sin</function>, which means that
-   <literal>a==sin(asin(a))</literal> for every value of a that is within
+   <code>$num == sin(asin($num))</code> for every value of a that is within
    <function>asin</function>'s range.
   </para>
  </refsect1>

reference/math/functions/atan.xml

@@ -15,7 +15,7 @@
    Returns the arc tangent of <parameter>num</parameter> in radians.
    <function>atan</function> is the inverse function of
    <function>tan</function>, which means that
-   <literal>a==tan(atan(a))</literal> for every value of a that is within
+   <code>$num == tan(atan($num))</code> for every value of a that is within
    <function>atan</function>'s range.
   </para>
  </refsect1>

reference/math/functions/expm1.xml

@@ -4,7 +4,7 @@
  <refnamediv>
   <refname>expm1</refname>
   <refpurpose>
-   Returns exp(number) - 1, computed in a way that is accurate even
+   Returns <code>exp($num) - 1</code>, computed in a way that is accurate even
    when the value of number is close to zero
   </refpurpose>
  </refnamediv>

reference/math/functions/hypot.xml

@@ -19,7 +19,7 @@
    right-angle triangle with sides of length <parameter>x</parameter> and
    <parameter>y</parameter>, or the distance of the point
    (<parameter>x</parameter>, <parameter>y</parameter>) from the origin.
-   This is equivalent to <literal>sqrt(x*x + y*y)</literal>.
+   This is equivalent to <code>sqrt($x*$x + $y*$y)</code>.
   </para>
  </refsect1>
  <refsect1 role="parameters">

reference/math/functions/round.xml

@@ -61,7 +61,7 @@
       <para>
        If the <parameter>precision</parameter> is negative, <parameter>num</parameter> is
        rounded to <parameter>precision</parameter> significant digits before the decimal point,
-       i.e. to the nearest multiple of <literal>pow(10, -precision)</literal>, e.g. for a
+       i.e. to the nearest multiple of <code>pow(10, -$precision)</code>, e.g. for a
        <parameter>precision</parameter> of -1 <parameter>num</parameter> is rounded to tens,
        for a <parameter>precision</parameter> of -2 to hundreds, etc.
       </para>