1/(sin(90 + θ)cos(360 - θ)) - tan²(-θ)
Note:
sin(90 + θ) = cosθ Cosine and Sine are complementary.
cos(360 - θ) = cosθ Cosine positive in 4th quadrant.
tan(-θ) = -tanθ Negative angle concept.
1/(sin(90 + θ)cos(360 - θ)) - tan²(-θ) = 1/(cosθcosθ) - (-tanθ)²
= 1/(cos²θ) - tan²θ
= (1/cosθ)² - tan²θ
Note: 1/cosθ = secθ
= (secθ)² - tan²θ
= sec²θ - tan²θ
= 1
Note that 1+ tan²θ = sec²θ is a Trigonometric identity.
That means: sec²θ - tan²θ = 1
Hope this explains it.