Question

cos²(π-α)+sin²(π/2-α)+cos(π+α)cos(2π-α)/tg²(α-π/2)ctg²(3π/2+α)=cos²α

Answer 1

 cos²α+cos²α+(-cosα*cosα)/ctg²αtg²α=cos²α/1=cos²α
 тождество верно