JAMB 1998 · UME · Q39

Differentiate $\dfrac{x}{\cos x}$ with respect to $x$ .

Worked solution (try it first)

Write $\dfrac{x}{\cos x} = x\sec x$ , and recall that $\sec x$ differentiates to $\sec x\tan x$ .
Product rule: $1 \cdot \sec x + x \cdot \sec x\tan x$ .
So the derivative is $\sec x + x\sec x\tan x$ , option D.