Piecewise functions have different definitions, depending on when you evaluate them.
Given an input x, your function returns:
- 2x if the input is negative
- 1 if the input lies between 0 (included) and 2 (excluded)
- the square root of x if the input is greater than 2 (included)
You want to know what f(0) is. In other words, you want to know what happens if we give 0 as input.
The piecewise definition tells us that, if the input is 0, the function outputs 1.
So, you have f(0) = 1.