∵AB⊥CD,三角形ABD是锐角三角形,过CD作平面垂直于AB,交AB于E,则CE⊥AB,DE⊥AB.∴DE^2=AD^2-AE^2=BD^2-BE^2,CE^2=AC^2-AE^2=BC^2-BE^2.∴AD^2-AE^2=BD^2-BE^2,AD^2-AE^2=BD^2-BE^2,AE^2= AD^2- BD^2+BE^2AC^2-AE^2=B...