The expression is true.
Step-by-step explanation:
Left Hand Side = 1/sec²k = cos²k
Right Hand Side = sin²k cos²k + cos^4k
= cos²k (sin²k + cos²k) (Taking cos²k as common)
= cos²k (∵sin²k + cos²k = 1)
⇒ Left Hand Side = Right Hand Side
So the expression is true.