Math: consistently use arccos() in math equations.

src/Magnum/Math/Complex.h

@@ -63,7 +63,7 @@ template<class T> inline T dot(const Complex<T>& a, const Complex<T>& b) {
 @brief Angle between normalized complex numbers
 
 Expects that both complex numbers are normalized. @f[
-    \theta = acos \left( \frac{Re(c_0 \cdot c_1))}{|c_0| |c_1|} \right) = acos (a_0 a_1 + b_0 b_1)
+    \theta = \arccos \left( \frac{Re(c_0 \cdot c_1))}{|c_0| |c_1|} \right) = \arccos (a_0 a_1 + b_0 b_1)
 @f]
 @see @ref Complex::isNormalized(),
     @ref angle(const Quaternion<T>&, const Quaternion<T>&),

src/Magnum/Math/Quaternion.h

@@ -66,7 +66,7 @@ namespace Implementation {
 @brief Angle between normalized quaternions
 
 Expects that both quaternions are normalized. @f[
-     \theta = acos \left( \frac{p \cdot q}{|p| |q|} \right) = acos(p \cdot q)
+     \theta = \arccos \left( \frac{p \cdot q}{|p| |q|} \right) = \arccos(p \cdot q)
 @f]
 @see @ref Quaternion::isNormalized(),
     @ref angle(const Complex<T>&, const Complex<T>&),
@@ -347,7 +347,7 @@ template<class T> class Quaternion {
          * @brief Rotation angle of unit quaternion
          *
          * Expects that the quaternion is normalized. @f[
-         *      \theta = 2 \cdot acos q_S
+         *      \theta = 2 \cdot \arccos(q_S)
          * @f]
          * @see @ref isNormalized(), @ref axis(), @ref rotation()
          */

src/Magnum/Math/Vector.h

@@ -86,7 +86,7 @@ template<std::size_t size, class T> inline T dot(const Vector<size, T>& a, const
 
 Expects that both vectors are normalized. Enabled only for floating-point
 types. @f[
-    \theta = acos \left( \frac{\boldsymbol a \cdot \boldsymbol b}{|\boldsymbol a| |\boldsymbol b|} \right) = acos (\boldsymbol a \cdot \boldsymbol b)
+    \theta = \arccos \left( \frac{\boldsymbol a \cdot \boldsymbol b}{|\boldsymbol a| |\boldsymbol b|} \right) = \arccos (\boldsymbol a \cdot \boldsymbol b)
 @f]
 @see @ref Vector::isNormalized(),
     @ref angle(const Complex<T>&, const Complex<T>&),