Question

What is the domain of the quadratic function given by f(x) = 2x2 + 2x - 4?

a.[0, +∞)
b.all real numbers
c.all negative real numbers
d.all positive real numbers?

Answer 1

b. All real numbers :)

The only conern here is that you are able to square x. Since the square of any real number gives a real number answer, then that is the domain.

If the function was
`√(x)`, then the domain woudl be all POSITIVE real numbers since you cannot take the square root of a negative number. Try it on your calculator! you will get an error! Domain simply means all possible values for x that actually give real number answers.

(the opposite of a real number is an imaginary number, like 'i' = [tex]\sqrt{-1}[tex]. You can see that you cannot sqrt a negative number, yet, in quantum mechanics 'i' is used all the time because it makes things work in calculations.