docs: public static BigDecimal acos(BigDecimal x, MathContext mathContext) {
  		checkMathContext(mathContext);
  		if (x.compareTo(ONE) > 0) {
  			throw new ArithmeticException("Illegal acos(x) for x > 1: x = " + x);
  		}
  		if (x.compareTo(MINUS_ONE) < 0) {
  			throw new ArithmeticException("Illegal acos(x) for x < -1: x = " + x);
  		}
  
  		MathContext mc = new MathContext(mathContext.getPrecision() + 6, mathContext.getRoundingMode());
  
  		BigDecimal result = pi(mc).divide(TWO, mc).subtract(asin(x, mc), mc);
  		return round(result, mathContext);
  	}