Tangent of Theta +90

This applet uses the original geometric definition of a tangent, where BC = tan [math] \theta[/math]. If you haven't seen this definition before, but know another definition, figure out why the definitions are equivalent.

Explain why [math]\triangle COB\sim \triangle ODB[/math]. Find the relationship between [math]\tan\theta[/math] and[math]\tan(\theta+90)[/math].