## GR8767 Q30

Forum for the GRE subject test in mathematics.
mathQ
Posts: 41
Joined: Thu Mar 25, 2010 12:14 am

### GR8767 Q30

Q) The improper integral INT [a,b] f(x) f'(x) dx is

A) necessarily zero
B) possibly 0 but not necessarily
C) necessarily non non existant
D) possibly non existant but not necessarily
E) none of the above

mrb
Posts: 25
Joined: Fri Oct 30, 2009 7:58 pm

### Re: GR8767 Q30

You need to give the function f. Don't expect people to go look stuff up for you.

origin415
Posts: 61
Joined: Fri Oct 23, 2009 11:42 pm

### Re: GR8767 Q30

mrb wrote:You need to give the function f. Don't expect people to go look stuff up for you.

The question is just as mathQ wrote it, a, b, and f are all arbitrary.

Back to the original: this problem can be simplified using substitution with u=f(x).

mathQ
Posts: 41
Joined: Thu Mar 25, 2010 12:14 am

### Re: GR8767 Q30

origin415 wrote:
mrb wrote:You need to give the function f. Don't expect people to go look stuff up for you.

The question is just as mathQ wrote it, a, b, and f are all arbitrary.

Back to the original: this problem can be simplified using substitution with u=f(x).

I tried that...that would give me the ans ( [f(b)]^2 - [f(a)]^2 )/ 2

is it some printing mistake on the ques paper ?

origin415
Posts: 61
Joined: Fri Oct 23, 2009 11:42 pm

### Re: GR8767 Q30

Okay, sorry, mrb is right, I went back and looked at the problem, at the top of the page it says

Let f be a function such that the graph of f is a semicircle S with end points (a,0) and (b, 0) where a < b

Its the same f which was used for the two previous questions.

Because of the endpoints, f(a) = f(b) = 0

Posts: 2
Joined: Tue May 25, 2010 12:14 am

### Re: GR8767 Q30

There are two more questions before this question and there is a statement before these questions. all three questions are related to this statement so see this question in view of that statement.