Internal bisector ∠A of △ABC meets side BC at D.A line drawn through D perpendicular to AD intersects the side AC at E & side AB at F. If a, b, c represent sides of △ABC, then
(a) AE is the HM of b & c
(b) \(AD =\frac{2bc}{b+c} cos \frac A2\)
(c) \(EF = \frac {4bc}{b+c} sin \frac A2\)
(d) △AEF is isosceles