Calculus (3rd Edition)

(a) $-, +$ (b) $+$ (c) $-$
a) Since the derivative of $\sin x$ is $\cos x$ and the derivative of $\cos x$ is $-\sin x$ then we have to choose the following signs: $-, +$. b) Since the derivative of $\sec x$ is $\sec x\tan x$ then we have to choose the following sign: $+$. c) Since the derivative of $\cot x$ is $-\csc^2 x$ then we have to choose the following sign: $-$.