Answer
-1.9
Work Step by Step
Two numbers that are the same distance from 0 but lie on opposite sides of 0 are called opposites of each other.
We know that the opposite of a number $a$ is $-a$, because $a+(-a)=a-a=0$.
Therefore, the opposite of 1.9 is -1.9, because $1.9+(-1.9)=1.9-1.9=0$.