Mathematics for IGCSE & O level - Pythagoras' Theorem And Trigonometry (Section 4 - No. 31)
For acute angles, what is the relationship between sin and cos?
sin(θ) = cos(90° + θ)
sin(θ) = cos(90° - θ)
sin(θ) = cos(180° + θ)
sin(θ) = cos(180° - θ)
Explanation
sin(θ) = cos(90° - θ), for acute angles.