GR8767 Q63

Forum for the GRE subject test in mathematics.
Posts: 11
Joined: Wed Oct 01, 2008 9:16 pm

GR8767 Q63

Postby kaiserguy » Tue Oct 14, 2008 8:27 pm

I've been working away on the sample tests but here's one question I just can't get. I'm pretty bad with inverse functions.

Firstly, let's call int(0,inf)[f] the integral from 0 to infinity of a function f.

Let f be a continuous, strictly decreasing, real-valued function such that int(0,inf)[f] is finite and f(0)=1. In terms of f^-1 (the inverse fucntion of f), int(0,inf)[f] is

(A) less than int(1,inf)[f^-1]
(B) greater than int(0,1)[f^-1]
(C) equal to int(1,inf)[f^-1]
(D) ANS equal to int(0,1)[f^-1]
(E) equal to int(0,inf)[f^-1]

Thanks in advance,

Posts: 42
Joined: Wed Sep 03, 2008 5:39 pm

Postby CoCoA » Tue Oct 14, 2008 8:36 pm

Think of f(x) as y, draw a graph of it. Your integral is the area bounded by the graph of f, the y axis, and the x axis. Refurmulate the integral with y as the variable.

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