证明题:sin(-α)sin(丌-α) -tan(-α)cot(α-丌)-2cos^2 (-α)+1=sin^2 α

sin(-α)sin(丌-α) -tan(-α)cot(α-丌)-2cos^2 (-α)+1
=-sin²α+1-2cos²α+1
=-sin²α+2-2cos²α
=sin²α+2sin²α
=sin²α
得证