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Mar 21, 2011 at 23:22 vote accept Jeff Morrow
Mar 21, 2011 at 22:46 comment added Will Jagy $$ 0 \geq \int_0^b (x-a) (f(x) - g(x)) dx = \int_0^b x (f(x) - g(x)) dx = \int_0^b x f(x) dx - \int_0^b x g(x) dx $$ See answer below by Charles Matthews.
Mar 21, 2011 at 22:20 history edited Will Jagy CC BY-SA 2.5
I gave it a shot; added 6 characters in body
Mar 21, 2011 at 22:16 comment added Jeff Morrow I do not know how to get the neat integrals, but the integral of g(x) from 0 to a = [a / (b + a)]. The integral of g(x) from a to b = (1/2)(b^2 - 2ab + a^2) / (b^2 - a^2) = (b - a) / 2(b + a). So the integral from 0 to b = [(2a + b - a) / 2(b + a)] = [(b + a) / 2(b + a)] = (1/2). If I have erred in integrating, I am ashamed because it is essential that the integral = 1/2.
Mar 21, 2011 at 22:00 comment added Jeff Morrow First, thank you for the type setting. That certainly is easier to read. Second, I believe that you have re-stated the problem correctly except "all possible k" may be confusing because k(x) = xg(x), and g(x) is fully defined so only one possible k(x) exists.
Mar 21, 2011 at 21:10 answer added Charles Matthews timeline score: 1
Mar 21, 2011 at 21:04 comment added KConrad I edited the question so it is easier to read mathematically. If I messed up any of the conditions when I changed the typesetting, please say so.
Mar 21, 2011 at 21:02 history edited KConrad CC BY-SA 2.5
added 59 characters in body; added 1 characters in body
Mar 21, 2011 at 16:18 history asked Jeff Morrow CC BY-SA 2.5