# CSE 525 (Spring 2019): HW #2

**Due: Thurs, Apr 18, 11:59pm**

## Problem 1: Random sums

Show there is a positive number such that the following holds.
For any real numbers satisfying ,
if are i.i.d. uniformly random signs,
then

[Hint: Consider the case separately.]

## Problem 2: Sensor deployment

Suppose you are designing the sensor deployment system for SpaceX’s
Mars exploration mission. In order to search for habitable land,
you will deploy sensor packets from the atmosphere. Each packet
is designed to disperse sensors uniformly over one square kilometer.
(So you can imagine that the sensors are placed uniformly and independently at random
in the unit square .)

The sensors will communicate with each other via a mesh network, but to
keep energy costs down, it’s important that every sensor communicates with
a very small number of other sensors. There is a parameter
such that every sensor can send messages to the closest sensors (in Euclidean distance;
you may assume that the sensors are deployed on flat ground).

You can think of the resulting directed graph : The vertices are sensors
and there is an edge between two sensors and if is one of
the closest sensors to . In order for the mesh network
to be intact, it should be that is strongly connected (in other words,
between every pair of sensors, there should be a directed path in ).

(a) Prove there is a constant such that if , then

(b) Prove there is a constant such that if , then

(c) [**Bonus**]: Establish a sharper threshold.
Prove that there is a constant such that if and