Why {-x}=1-{x} where {x} is the fractional part of x

Let's proceed with an example.

Let's assume x= 2.3

So {x}={2.3}=0.3

Now, {-x}={-2.3}=-2.3+3 = 0.7

[to Know why I add 3 instead of taking -0.3 as fractional part please refer my previous post 

why for -2< x< -1 the fractional part is x+2 ]

So simply you can see 0.7+0.3=1

In other words, {x}+{-x}=1

So, {-x}=1-{x}