Chapter 3 - Differentiation - 3.6 Trigonometric Functions - Preliminary Questions - Page 139: 1

(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: $-$.