Question

f(x)=-5x+4 find the domain of a function?

Answer 1

the domain are all the valid values x can have
for this function, all x values are allowed.

here is an example where x=0 is not allowed
f(x)= 1/x ( because dividing by 0 is not allowed)

here is one where x must be ≥0 (0 or bigger)
f(x)= sqrt(x) (because you are not allowed to take the sqrt of neg numbers)

Answer 2

Honestly I did not understand the concept at all. The answer in the book is all real numbers? how we find it?

Answer 3

The idea is that f(x) has a value for every (valid) x. Unless you know otherwise, all x are valid.

In other words, for any x you can think of, if you put that value into your expression, you can find f(x). The domain is (-infinity, +infinity) or all real numbers.

However, there are functions where this will not be true. See my post for such examples.

Answer 4

how will u find this one?

Answer 5

I wrote it another question