如图,在梯形ABCD中,AD平行于BC,AB=CD,对角线AC垂直BD于点O,AD=3,BC=5,求AC的长{写出计算过程}
过D作DE//AC ,交BC延长线于E ,因AC垂直并等于BD ,故DE垂直并等于BD ,BE=8
故 AC=(√ 2/2)*BE = 4√ 2