d x = 2 1 + t 2 d t d t d x = ( 1 cos 2 x 2 ) ⋅ ( x 2 ) ′ d t d x = ( 1 + tan 2 x 2 ) ⋅ ( x 2 ) ′ d x = 2 1 + tan 2 x 2 d t