數 直線方程

Let A be ( r cos t, r sin t) and B be ( - r sin t, r cos t)
Using the 2 points form formula,
(y - r cos t)/(r sin t - r cos t) = (x + r sin t)/(r cos t + r sin t)
(y - r cos t)(r cos t + r sin t) = (x + r sin t)(r sin t - r cos t)
y( cos t + sin t) - r cos^2 t - r cos t sin t = x(sin t - cos t) + r sin^2 t - r sin t cos t
y( cos t + sin t) = x( sin t - cos t) + r is the equation of the line AB.