Question 46289
If x is one of two numbers whose sum is 30, then the other number is 30-x, since x + (30-x) = 30

The product of x and (30-x) is:
{{{x(30-x) = 30x - x^2}}}

A function of x representing this can be written:
{{{f(x) = 30x-x^2}}}