f(x)上的点到x-y-3=0的距离＝｜x-a^2x^2-3|/根号2＝｜a^2x^2-x+3|/根号2a^2x^2-x+3=a^2(x-1/2a^2)+3-1/(4a^2)当x=1/(2a^2)时有最小值是3-1/(4a^2)即|3-1/4a^2|/根号2＝根号2｜3-1/4a^2|=23-1/4a^2=2或－21/4a^2=1或5...