1992年高考第(13)题是: 已知直线l_1和l_2夹角的平分线为y=x,如果l_1的方程是ax+by+c=0(ab>0),那么l_2的方程是 (A)bx+ay+c=0;(B)ax-by+c=0; (C)bx+ay-c=0;(D)bx-ay+c=0。标准卷上选(A)。但明显,这四个选择支都是欠妥的。直线l_1:ax+by+c=0(ab>0),所以斜率k=-a/b<0,如图1所示,不妨固定平面上某一点A,则l_1只能 The (13) title of the 1992 college entrance examination was: The bisector of the angle between the known lines l_1 and l_2 is y=x. If the equation of l_1 is ax+by+c=0 (ab>0), then the equation for l_2 is ( A) bx+ay+c=0; (B) ax-by+c=0; (C) bx+ay-c=0; (D) bx-ay+c=0. The standard volume was selected (A). Obviously, these four options are all defective. Line l_1:ax+by+c=0 (ab>0), so the slope k=-a/b<0, as shown in Figure 1, you can fix a point A on the plane, then l_1 can only