分别过点A、C作AM⊥BD于M,CN⊥BD于N∵∠ABC=∠ADC=90°,即四边形ABCD对角互补∴A、B、C、D四点共圆又,AD=CD∴∠ABD=∠CBD = (1/2)*90° = 45° （若两条弦相等,则所对应的圆心角相等）∴AM=BM = (1/√2)AB,CN=BN = (...