the slope of a curve y=f(x) is given by

dy/dx= (x-1)(x-2)^2(x-3)^3(x-4)^4(x-5)^5

for what value or values of x does y have a local maximum/miniumum? justify your answer.

i tried solving this question but couldn't figure out how to do it. i even asked my old maths school teacher but even she couldn't solve it. could anyone please help me!!! thanks very much

2 answers

since y'=0 at x=1,2,3,4,5 the max/min can occur there.

But, y' has roots of even multiplicity at x=2 and 4, so those will be inflection points.

So, extrema will occur at x=1,3,5

Why? The slope has to change sign at the extrema. If y' has roots of even multiplicity, it does not change sign there, but only magnitude.
thank you so much for your help