The sag in a beam of length L, width w and height h (see Figure 12.23) is given by S(L , w , h) = c L^4/〖wh〗^3 for some constant c. Show that ∂S/∂L= 4/L S,∂S/∂W=-1/W S and ∂S/∂h=-3/h s Use this result to determine which variable has the greatest proportional effect on the sag.
Solution We start by computing