17. 直线(2a+1)x−ay−1=0(2a+1)x-ay-1=0(2a+1)x−ay−1=0被曲线x2+y2−2x−2y=0x^{2}+y^{2}-2x-2y=0x2+y2−2x−2y=0截得的弦长的最小值为((( )))