Question 901044
Prove the identity: 
(Cosx /1-sinx) - (cosx/1+sinx) =2tanx
start with left side:
{{{cos(x)/(1-sin(x))-cos(x)/(1+sin(x))}}}
{{{(cos(x)(1+sin(x))-cos(x)(1-sin(x)))/(1-sin^2(x))}}}
{{{(cos(x)(1+sin(x))-cos(x)(1-sin(x)))/(cos^2(x))}}}
{{{(1+sin(x)-(1-sin(x)))/(cos(x))}}}
2sin(x)/cos(x)=2tan(x)
verified: left side=right side