The question accepts
$$
\frac{-3\sin(3\csc(2\sqrt{u}))\csc(2\sqrt{u})\cot(2\sqrt{u})}{\sqrt{u}}
$$
when the answer should be positive
$$
\frac{3\sin(3\csc(2\sqrt{u}))\csc(2\sqrt{u})\cot(2\sqrt{u})}{\sqrt{u}}
$$
See chainRule/exercises/harderChainRule1.tex
The question accepts
when the answer should be positive
See chainRule/exercises/harderChainRule1.tex