@Override
  protected DoubleWritable doEvaluate(DoubleWritable a) {
    double d = a.get();
    if (d < -1 || d > 1) {
      return null;
    } else {
      result.set(StrictMath.asin(d));
      return result;
    }
  }
Take Arc Sine of a in radians.
ql/src/java/org/apache/hadoop/hive/ql/udf/UDFAsin.java