∵ABCD是菱形
∴∠BAD+∠B=180°
∵∠BAD=2∠B即∠B=1/2∠BAD
∴∠BAD+1/2∠BAD=180°
∠BAD=120°
2、∵∠BAD=120°
∴∠B=60°
∵AB=CB
∴△ABC是等边三角形