用三角代换
设x=4cosθ,y=2sinθ
则椭圆x2/16+y2/4=1上的点到直线x+2y-根号2=0的距离为:
|4 cosθ+4 sinθ-√2|/√5=|4√2sin(θ+π/4)- √2|/√5≤|-4√2- √2|/√5=√10.