Answer:
sin2A +cos2A=1. Its a standard identity.
We know that sinA= H B
--- and cos A=----
P H
Hence sin² A= P² B²
----- and cos²A -----
H² H²
Hence adding the above given functions sin²A+cos²A we get
H²
sin²A+cos²A = -------- =1
H²
Using P² +B²=H² by Pythagoras Theorem
