Which of the following is equal to secA - cosA?

Answer: Option A

$$\begin{array}{rl}& \sec A-\cos A\\ & =\frac{1}{\cos A}-\cos A\\ & =\frac{1-{\cos }^{2}A}{\cos A}\\ & =\frac{{\sin }^{2}A}{\cos A}\\ & =\tan A.\sin A\end{array}$$