2tan^-1x = cos^-1(1-x^2/1+x^2)
tan-1x = y
x= tany
2tan-1x= cos-1 1-x2/1+x2
= cos-1 1-tan2y/1+tan2y
= cos-1(cos2y)
=2y
=2tan-1x
therefore, 2tan-1x = cos-1 1-x2/1+x2
2tan^-1x = cos^-1(1-x^2/1+x^2)
tan-1x = y
x= tany
2tan-1x= cos-1 1-x2/1+x2
= cos-1 1-tan2y/1+tan2y
= cos-1(cos2y)
=2y
=2tan-1x
therefore, 2tan-1x = cos-1 1-x2/1+x2