a|=根号(1+0)=1 |b|=根号(2+1)=根号5 a*b=1×2+0×1=2 |a+3b| =a+6ab+9b =1+6×2+9×5 =58 |a+3b|=根号58 ka-b=(k-2,-1) a+3b=(7,3) ka-b与a+3b平行,则有 (k-2)×3-(-1)×7=0 3k-6+7=0 k=-1/3 此时,ka-b与a+3b反向 ...