25.已知体积为6的四面体ABCDABCDABCD满足AB⊥BCAB\bot BCAB⊥BC,BC⊥CDBC\bot CDBC⊥CD,AB=BC=CD=23AB=BC=CD=2\sqrt{3}AB=BC=CD=23,则异面直线ADADAD与BCBCBC所成的角的大小为 ___π4\frac{\pi }{4}4π[或]π3\frac{\pi }{3}3π___.