Proof of Diameter Chord Formula Print In the diagram below the diameter AC bisects the chord BD at right angles.In the bottom diagram \[xy=d^2\] To prove this notice that AC is a diamter so ABC is a right angle.\[tan \theta = \frac{d}{y} = \frac{x}{d} \] Hence \[xy=d^2\] Prev Next Add comment Name (required) E-mail (required, but will not display) Refresh SendCancel