In my React project, I need a variable that depends on two state variables. Do I need to use useState for this variable, or only for the variables it depends on?

For example, is this design pattern possible:

const [number1, setNumber1] = useState(2); const [number2, setNumber2] = useState(2); const sum = number1 number2; 

Or do I need to create sum as state and update it with useState when number1 or number2 changes (e.g. in useEffect callback)?