# [SOLVED]Max and min of discrete model

#### dwsmith

##### Well-known member
To find the max and min of a discrete model, I solve

$$\frac{df}{dN_t} =0\Rightarrow N_m$$
Then $N_{\text{max}} = f(N_m)$, correct?

Because whenever I try to solve

$$N_{t+1} =\frac{(1+r)N_t}{1+rN_t}$$

It doesn't work.

The derivative is
$$\frac{1+r}{(1+rN_t)^2}=0$$