diff --git a/math/sin.c b/math/sin.c
new file mode 100644
index 0000000..867604b
--- /dev/null
+++ b/math/sin.c
@@ -0,0 +1,5 @@
+#include <math.h>
+
+double sin(double x) {
+  return cos(x - M_PI_2);
+}
\ No newline at end of file