We need
cos^2x=1-sin^2x
Therefore,
int(tanxdx)/(1-sinx)=int(sinxdx)/(cosx(1-sinx))
=int(sinxcosxdx)/(cos^2x(1-sinx))
=int(sinxcosxdx)/((1-sin^2x)(1-sinx))
=int(sinxcosxdx)/((1+sinx)(1-sinx)^2)
Perform the substitution
u=sinx, =>, du=cosxdx
Therefore,
int(tanxdx)/(1-sinx)=int(udu)/((1+u)(1-u)^2)
Perform the decomposition into partial fractions
u/((1+u)(1-u)^2)=A/(1+u)+B/(1-u)^2+C/(1-u)
=(A(1-u)^2+B(1+u)+C(1+u)(1-u))/(((1+u)(1-u)^2))
The denominators are the same, compare the numerators
u=A(1-u)^2+B(1+u)+C(1+u)(1-u)
Let u=-1, =>, -1=4A, =>, A=-1/4
Let u=1, =>, 1=2B, =>, B=1/2
Coefficients of u^2
0=A-C, =>, C=A=-1/4
Therefore,
u/((1+u)(1-u)^2)=(-1/4)/(1+u)+(1/2)/(1-u)^2+(-1/4)/(1-u)
So,
int(tanxdx)/(1-sinx)=int(-1/4du)/(1+u)+int(1/2du)/(1-u)^2+int(-1/4du)/(1-u)
=-1/4ln(1+u)-1/2*1/(1-u)+1/4ln(1-u)
=-1/4ln(1+sinx)-1/(2(1-sinx))+1/4ln(1-sinx)+C