l1:3x-y-2=0,l2:x+2y-6=0直线斜率k1=3,k2=-1/2根据直线的夹角公式tanθ=|(k2-k1)/(1+k2k1)| =|(-1/2-3)/(1-3/2)| =7∴l1与l2的夹角为arctan7
