Derivative word problems are usually problems in maximizing or minimizing
some function of x by taking the derivative, and setting it to zero to find the
maximum or minimum of the function.
Minimum perimeter of an isosceles triangle — given
an isosceles triangle with area 1, what is the length of the base that minimizes
the perimeter? We find the answer by expressing the perimeter, P, in terms
of the base, b, and then finding the derivative of P with respect to b.