# A calculus problem by Christopher Boo

Calculus Level 3

$\begin{array} {l c l } \dfrac d{dx} \cos x &= &- \dfrac d{dx} \sin x \\ \dfrac d{dx} (\cos x)^2 &=&- \dfrac d{dx}(\sin x)^2 \\ \dfrac d{dx} (\cos x)^3 &=& - \dfrac d{dx}(\sin x)^3 \end{array}$

Which of the equations above is an identity?

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