In parallelogram ABCD, two adjacent sides' ratio is 2:5.Perimeter=28cm.BE.CF bisect angleABC and angle BCD to meet E,F on AD respectively.Length of EF is?
In parallelogram ABCD, two adjacent sides' ratio is 2:5.Perimeter=28cm.BE.CF bisect angleABC and angle BCD to meet E,F on AD respectively.Length of EF is?
已知一等腰梯形的两底边长的差等于一腰的长，那麽它的腰和下底的夹角是?