直线x+a^2y+1=0与直线(a^2+1)x-by+3=0相垂直 则: (-1/a^2)*(a^2+1)/b = -1 b*a^2=a^2+1 ... b=1+1/a^2 ab=a+1/a a=1/a时,|ab|最小! |ab|=2
