Question

求微分dy是求微分吧,那最后还要加个dx了?

Answer 1

y=cos^3(1/x)

y'=3cos^2(1/x)(cos1/x)'

=3cos^2(1/x)[-sin(1/x)](1/x)'

=-3cos^2(1/x)*[-sin(1/x)]*(-1/x^2)

=3cos^2(1/x)*[sin(1/x)]/(x^2)

dy=3cos^2(1/x)*[sin(1/x)]/(x^2)dx