Question

Which function’s domain consists of all real numbers greater than 3?
f(x)=3x
f(x)=√x
f(x)=3x+4
f(x)=1/√x-3

Answer 1

@amistre64

Answer 2

@amistre64

Answer 3

what does the domain tell us when dealing with functions?

Answer 4

all possible input values?

Answer 5

wait, they represent the possible output values.

Answer 6

had it right the first time.. input values

f(x) has a range that is dependant on x (its domain values)

Answer 7

so, knowing this, how would you propose we reach a solution

Answer 8

Put in values for x.

Answer 9

yes, but more specifically, lets pick a value that is NOT in the domain and see if the functions hold together or not.

is x=0 in the domain?

Answer 10

No. ?

Answer 11

if x=a is in the domain, then f(a) is defined.

this has the same truth value as:

if f(a) is NOT defined, then x=a is NOT in the domain.
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domain is: x > 3

since 0 > 3 is false, 0 is NOT in the domain

if f(0) is NOT defined, then we have determined the proper function

Answer 12

Oh, okay.

Answer 13

So should I plug in all x for 0 and see which one is greater than 3?

Answer 14

no, you should do like i suggested

put in 0 for all xs, and see which function makes no sense ... is undefined.

Answer 15

That leaves all of them except for the 3rd option. Is that correct?

Answer 16

correct

1/sqrt(-3) is not defined; or at least its not a defined real number.

Answer 17

Thanks !

Answer 18

yw