Prove the identity

[theocoleone]

1-) prove cos² (a-90)+ctg²(a-270) = 1/sin²(a+90) -cos²(a+180)

 

[Deleted member 4993]

1-) prove cos² (a-90)+ctg²(a-270) = 1/sin²(a+90) -cos²(a+180)

Hint:

Expand

1. cos(Θ-90) and cos(Θ+180) in terms of cos(Θ) and/or sin(Θ)
   
   
2. ctg(Θ - 270) in terms of cos(Θ) and/or sin(Θ)
   
   
3. sin(Θ + 90) in terms of cos(Θ) and/or sin(Θ)