In triangular ADC, according to the large angle to the large side, the maximum DE is DC, and E and C coincide, so

AD & ltDC=3, (when the triangle is an equilateral triangle of ADC, AD=DE(E and C coincide))

2.AD≧DF(DF is the distance from d to BC)

(if ad

AD≧( 1/2)*(6-AD) Angle B = 30, DF=( 1/2)BD.

Solving AD≧2

So 2 ≦ ad