Please help if you know trig, will give brainliest! Thank you!

Answer:
sin^2(a) I believe. Delete my response if needed.
Step-by-step explanation:
tan²(α) (2 cos²(α) + sin²(α) - 1)
Recall that sin²(α) + cos²(α) = 1 for all α. Then sin²(α) - 1 = -cos²(α) :
tan²(α) (2 cos²(α) - cos²(α))
tan²(α) cos²(α)
Rewrite tan(α) = sin(α) / cos(α) :
(sin(α) / cos(α))² cos²(α)
(sin²(α) / cos²(α)) cos²(α)
Cancel the factors of cos²(α) :
sin²(α)