Answer
$(A)$
$\tan{x}\sec{x}\cos{x}= \tan{x}$
Work Step by Step
To find out which expression is not equivalent to $1$, let's go through each of the expressions $1$ by $1$ and simplify them.
Note, we will use trigonometric identities.
$(A)$
$\tan{x}\sec{x}\cos{x}= \tan{x}\frac{1}{\cos{x}}\cos{x} = \tan{x}$
As we can see it is not equivalent to $1$, so we have found the answer.
So we do not have to go through other expressions.
