MathDB
Putnam 1991 A5

Source:

October 9, 2006
Putnamintegrationcalculusinequalitiesfunctioncollege contests

Problem Statement

A5) Find the maximum value of 0yx4+(yy2)2dx\int_{0}^{y}\sqrt{x^{4}+(y-y^{2})^{2}}dx for 0y10\leq y\leq 1. I don't have a solution for this yet. I figure this may be useful: Let the integral be denoted f(y)f(y), then according to the [url=http://mathworld.wolfram.com/LeibnizIntegralRule.html]Leibniz Integral Rule we have dfdy=0yy(1y)(12y)x4+(yy2)2dx+y4+(yy2)2\frac{df}{dy}=\int_{0}^{y}\frac{y(1-y)(1-2y)}{\sqrt{x^{4}+(y-y^{2})^{2}}}dx+\sqrt{y^{4}+(y-y^{2})^{2}} Now what?