What is tan squared theta minus sec squared theta simplified?

tan θ = sin θ / cos θ

sec θ = 1 / cos θ

sin ² θ + cos² θ = 1 → sin² θ - 1 = - cos² θ

→ tan² θ - sec² θ = (sin θ / cos θ)² - (1 / cos θ)²

= sin² θ / cos² θ - 1 / cos² θ

= (sin² θ - 1) / cos² θ

= - cos² θ / cos² θ

= -1