diff --git a/base/special/fast/acosh/README.md b/base/special/fast/acosh/README.md
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+* * *
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+## C APIs
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+### Usage
+
+```c
+#include "stdlib/math/base/special/fast/acosh.h"
+```
+
+#### stdlib_base_fast_acosh( x )
+
+Computes the [hyperbolic arccosine][inverse-hyperbolic] of a double-precision floating-point number.
+
+```c
+double out = stdlib_base_fast_acosh( 1.0 );
+// returns 0.0
+
+out = stdlib_base_fast_acosh( 2.0 );
+// returns ~1.317
+```
+
+The function accepts the following arguments:
+
+- **x**: `[in] double` input value.
+
+```c
+double stdlib_base_fast_acosh( const double x );
+```
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+### Examples
+
+```c
+#include "stdlib/math/base/special/fast/acosh.h"
+#include
+
+int main( void ) {
+ const double x[] = { 1.0, 1.45, 1.89, 2.33, 2.78, 3.22, 3.66, 4.11, 4.55, 5.0 };
+
+ double v;
+ int i;
+ for ( i = 0; i < 10; i++ ) {
+ v = stdlib_base_fast_acosh( x[ i ] );
+ printf( "acosh(%lf) = %lf\n", x[ i ], v );
+ }
+}
+```
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