The dissipation of heat through a composite material of width w centimetres can be modelled by the function

f(w) = 10/w - 0.77ln(w) – 3.2

You are required to find the width of material that will prevent any heat dissipation.

- I understand f(w)= 0, but I'm unsure of the next bit.

Show, by a sign change search, that this equation has a root lying in the interval 2 ≤ w ≤ 3

calculate f(2) and f(3)

If the value changes sign, then the graph must cross the w axis somewhere in the interval, since f(w) is continuous there.