Numerator : getNum

getNum takes as argument a rational fraction and returns the numerator of this fraction. Unlike numer, getNum does not simplify the fraction before extracting the numerator.
Input :

getNum((x^2-1)/(x-1))

Output :

x^2-1

Input :

getNum((x^2+2*x+1)/(x^2-1))

Output :

x^2+2*x+1