将平面直角坐标系以x轴为棱折成直二面角,则该坐标系中的直线y=x-1被折成的角的大小是_________________. 答案:解析:如图所示,AD=DB=BE=EC=1, B是直线y=x-1与x轴的交点,显然BC=,AB=,连结AE,则CE⊥AE, ∴AC==. 在△ABC中,由余弦定理得cos∠ABC===-, ∴∠ABC=120°.答案:120°--Hello! May I speak to Tony,please? --Sure. . A.I'd love to B.I am afraid not C.Hold on,please