Does the graph represent a function? Please help. Look at photo

A function is defined as an operation on a number, which gives only one output for every input

while graphing a function, the x-ordinate denotes the input and the y-ordinate denotes the output of the function

Now, lets look at the graph

for the input value '4' , we notice that there are 2 possible outputs. The output can be either 2.5 or -2.5

Since there are multiple outputs for almost every input, this graph cannot denote a function since a function gives only one output