**4th case:** cos x> cos a (cos x cos a)

**5th case:** tg x <tg a (tg x tg a)

The general solution in IR can be expressed by .

The solution set is therefore:

**6th case:** tg x> tg a (tg x tg a)

Let's study the latter case by solving the inequality tg x> tg for example.

The general solution in IR can be expressed by

.

The solution set is therefore:

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