In the adjoining figure, if AD, AE, and BC are tangents to the circle at D, E, and F respectively, which of the following is true?
2AD=AB+BC+CA
We know that
AD=AE
AD=AB+BE
BE=BF are tangents drawn from the external point B to a circle, so BE=BF.
AD=AB+BF … (1)
Also,
AD=AC+CD
AD=AC+CF ……(2) (CD and CF are tangents drawn from the external point C to the circle)
Adding equations (1) and (2),
AD+AD=AB+BF+CF+AC
2AD=AB+BC+AC