摘要
题 如图所示,在矩形ABCD中,A<sub>1</sub>E∥AB,AA<sub>1</sub>=A<sub>1</sub>A<sub>2</sub>=A<sub>2</sub>A<sub>3</sub>=A<sub>3</sub>A<sub>4</sub>=A<sub>4</sub>D=a,AB<sub>1</sub>=B<sub>1</sub>B<sub>2</sub>=B<sub>2</sub>B=3<sup>1/2</sup>a, 求证:∠B<sub>1</sub>A<sub>1</sub>
