例、求证(tanx)=secx,(cscx)=- csc x cot x 证:(tanx)y sin x_(sin x)'cos x-sin x(cos x) COSX COS X cos x+sin x COs X (sin x) COS x (cSc x) Sin x SIn x cscx cotx 类似可证:(cotx)=-csc2x,( sec x)= secx tan x例、 (csc x) =        sin x 1 x 2 sin = − (sin x) x 2 sin = 求证 证:         = x x x cos sin (tan ) = x 2 cos (sin x)cos x − sin x (cos x) = x 2 cosx 2 cos x 2 + sin x 2 = sec − cos x = −csc xcot x 类似可证: (cot ) csc , 2 x  = − x (sec x) = sec x tan x