Chapter 4.3 Find the maximum product of two numbers (not necessarily integers) that have a sum of 100.

fx <- function(x) {
  x * (100-x)
}

fx1 <- Deriv(fx)
root <- uniroot(fx1, c(100, -100))
fx(root$root)
## [1] 2500
root$root
## [1] 50