Equation of the chord joining any two points on a hyperbola

Hyperbola
Equation x²/a² - y²/b² = 1

Two points are P(a sec θ1, b tan θ1) and Q(a sec θ2, b tan θ2)

Equation of the chord joining two points P and Q is

y - b tan θ1 = (x - a sec θ1)[b tan θ2 - b tan θ1]/[a sec θ2-a sec θ1]