As shown in the figure: in △ ABC, BC = 5, extend BC to point D, so that ∠ DAC = ∠ B, ad = 6, then CD=______ .

As shown in the figure: in △ ABC, BC = 5, extend BC to point D, so that ∠ DAC = ∠ B, ad = 6, then CD=______ .

∵∵∵ DAC = ∵ B, ∵ d = ∵ D, ∵ abd ∵ CAD, ∵ adcd = bdad, ∵ BC = 5, ad = 6, ∵ (5 + CD) CD = 36, that is, CD = 4