Solución
Tangente horizontal en
(
±
2
,
π
6
)
,
(
±
2
,
−
π
6
)
(±\sqrt{2},\frac{\pi}{6}),(±\sqrt{2},-\frac{\pi}{6})
(
±
2
,
6
π
)
,
(
±
2
,
−
6
π
)
.