Calculate fractional exponent/power, a^(num/den), where a could be negative.
a^(num/den)
## S3 method for class 'frac' exp(a, num, den)
a
numeric(1), base (could be negative).
numeric(1)
num
a positive integer, numerator of the exponent.
integer
den
a positive integer, denominator of the exponent.
numeric, the evaluated a^(num/den)
numeric