Barron SAT Math II page 15 #21.

If a and b are the domain of a function and f(b)<f(a), which of the following must be true?

a) b<a

b) b<a (error)

c) a=b

d)a ≠ b

e) a=0 or b=0.

The answer is d). Why? Why isn't it a)?

Thanks in advance

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- Oct 17th 2008, 06:21 AM #1

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## [SOLVED] f(b)<f(a)

Barron SAT Math II page 15 #21.

If a and b are the domain of a function and f(b)<f(a), which of the following must be true?

a) b<a

b) b<a (error)

c) a=b

d)a ≠ b

e) a=0 or b=0.

The answer is d). Why? Why isn't it a)?

Thanks in advance

- Oct 17th 2008, 07:12 AM #2

- Joined
- Jun 2008
- Posts
- 792

We rule out a because it is not always the case. You don't know if the function is increasing or decreasing.

We rule out c because if it was true, the function in question wouldn't be a function.

We're also not sure about e as well. It is possible, but we don't know for sure.

But the one you are 100% sure of is that d) they are not equal. If they were equal, then we have a contradiction.