Hi,

Question from SAT Subject Test Math 2. Hope you can answer it.

If f(x)=sqrt (x^2), then f(x) can also be expressed as:

A. x

B. -x

C. +/- x

D. modulus x

E. f(x) cannot be determined because x is unknown.My answer was A, but the given answer is C. Could you please explain?

The best way to explain, I think, is to point out what happens when *x* = –2:

So *f*(–2) = 2. In other words, when *x* = –2, then *f*(*x*) = –*x*. Of course, *f*(2) is ALSO equal to 2, so *f*(*x*) can also just be equal to *x*.

That’s why you have to say *f*(*x*) = ±*x*.