code: public static BigDecimal atan(BigDecimal x, MathContext mathContext) {
  		checkMathContext(mathContext);
  		MathContext mc = new MathContext(mathContext.getPrecision() + 6, mathContext.getRoundingMode());
  
  		x = x.divide(sqrt(ONE.add(x.multiply(x, mc), mc), mc), mc);
  
  		BigDecimal result = asin(x, mc);
  		return round(result, mathContext);
  	}
docs: Calculates the arc tangens (inverted tangens) of {@link BigDecimal} x.
  
  <p>See: <a href="http://en.wikipedia.org/wiki/Arctangens">Wikipedia: Arctangens</a></p>
  
  @param x the {@link BigDecimal} to calculate the arc tangens for
  @param mathContext the {@link MathContext} used for the result
  @return the calculated arc tangens {@link BigDecimal} with the precision specified in the <code>mathContext</code>
  @throws UnsupportedOperationException if the {@link MathContext} has unlimited precision