On Wednesday, April 30, 2014 5:02:27 AM UTC+2, William Elliot wrote: > On Tue, 29 Apr 2014, konyberg wrote: > > > > Find the largest values of the integer a for which ax^2-5x-3 is negative for all values of x. > > > set a = (5x + 3) / x^2 and find the minima of this function. This will, with > > > your constraints, give the answer: a = -3 > > 5/x + 3/x^2 > > -5/x^2 - 6/x^3 = 0 > > -5x + -6 = 0 > > x = -6/5 > > a = (-6 + 3)/(36/25) = -25/12 > > Why does the minimum work?
Are you asking me why it works? Or is it a retorical question to the OP? I know why it works :)