Right-Triangle Ratios
SOH-CAH-TOA, and what each ratio actually measures.
Concept
Three ratios, one triangle
Relative to an acute angle θ: sine is opposite/hypotenuse, cosine is adjacent/hypotenuse, tangent is opposite/adjacent.
Because they are ratios, they depend only on the angle — not on how big the triangle is. That is why a table of values works at all.
sin θ = O/H · cos θ = A/H · tan θ = O/A