find dy/dx
​y=log((1-x2)/(1+x2))

y = log(  ( 1 – x2) / ( 1 + x2) )
Or y = log( 1 – x2) – log( 1 + x2)      [log(a/b) = loga – logb ]
Now differentiating , dy/dx = ( 1/ 1 - x2) ( d/dx( 1 - x2) )     - ( 1/ 1 + x2)( d/dx( 1 + x2))            [Chain rule]
or dy/dx  = (1/1-x2)( -2x)    -   ( 1/1 + x2)(2x)
= -2x(   1 + x2 + 1 – x2 ) / ( 1 – x2) ( 1 + x2 )
= -4x/( 1 – x4 )
Hope that helps.
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