>>509
あほか
y'=-(tan(2x-1))'/tan^2(2x-1)
(tan(2x-1))'=2/cos^2(2x-1)だから
y'=-(2/cos^2(2x-1))×(1/tan^2(2x-1))
=-(2/cos^2(2x-1))×(cos^2(2x-1)/sin^2(2x-1))
=-2/sin^2(2x-1)