41. 已知直线:l1:y=ax+3l_{1}:y=ax+3l1:y=ax+3与l2l_{2}l2关于直线y=xy=xy=x对称,l2l_{2}l2与l3:x+2y−1=0l_{3}:x+2y-1=0l3:x+2y−1=0平行,则a=(a=(a=( )))