inttanx/(1-sinx)?

2 Answers

I=1/2sec^2x+[1/2secxtanx-1/2*ln(secx+tanx)]+C

Explanation:

I=int(tanx)/(1-sinx)dx

Divide each, numerator and denominator by cosx

=int(tanx/cosx)/(1/cosx-sinx/cosx)dx

=int(secxtanx)/(secx-tanx)dx

Multiply and divide the expression by (secx+tanx)

=int((secxtanx)(sec+tanx))/((secx-tanx)(sec+tanx))dx

rArrint((secx+tanx)secxtanx)/(sec^2x-tan^2x)dx

as, color(magenta)(sec^2x-tan^2x=1

rArrint(secx+tanx)xxsecxtanxdx

Let, color(red)(secx=t, therefore ,secxtanxdx=dt

rArrI=int(t+sqrt(t^2-1))dt

=intt.dt+intsqrt(t^2-1).dt

Applying, color(green)(intsqrt(X^2-a^2)dX=X/2sqrt(X^2-a^2)-a^2/2*ln|X+sqrt(X^2-a^2)|+C

=t^2/2+[t/2sqrt(t^2-1)-1/2*ln(t+sqrt(t^2-1))]+C

Replacing , t=secx

rArrI=sec^2x/2+[secx/2sqrt(sec^2x-1)-1/2*ln|secx+sqrt(sec^2x-1|)]+C

rArrI=sec^2x/2[1/2secxcolor(magenta)(tanx)-1/2*ln |secx+color(magenta)(tanx)|]+C

Mar 2, 2018

The answer is =-1/4ln(1+sinx)-1/(2(1-sinx))+1/4ln(1-sinx)+C

Explanation:

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