To learn how to format using only text, tryhere. My guess as to your meaning, using LaTeX formatting, is as follows:

. . . . .

A good way to start might be to split the addition into two parts, also converting the reciprocal of the secant into a cosine:

. . . . .

You learned an important trig limit, probably when you were learning trig derivatives:

. . . . .

With this in mind, restate the limit as:

. . . . .

The cosine can be simply evaluated, and the sine fraction is the limit they gave you earlier.