3.点(x0,y0)到直线Ax+By+c=0的距离公式d=|Ax0+By0+C|/√(A²+B²),
故点(x,y)到直线x+2y-16=0的距离是|x+2y-16|/√(1²+2²)=|x+2y-16|/√5.