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题59如图1,BC的模是AB模的k倍,BC的方向由AB的方向逆时针旋转θ角得到,则我们称AB经过一次(θ,k)延伸得到BC.设OA1=(1,0).
Problem 59 As shown in Fig. 1, the mode of BC is k times of AB mode, and the direction of BC is obtained by rotating the angle θ from the direction of AB counterclockwise. Then we call AB to extend BC once by (θ, k). Let OA1 = (1 , 0).