public Rational reciprocate() {
if (zero(num)) throw new ArithmeticException("Divide by zero");
Rational rv = new Rational(this);
rv.flip();
if (negative(den)) {
rv.num = rv.num.negate();
rv.den = rv.den.negate();
}
return rv;
}
public Rational divide(Rational b) {
Rational rv = new Rational(b);
rv.flip();
rv.mulEq(this);
return rv;
}