Final answer:
The formula for increments in the function u=f(x,t) is Δu = ∂u/∂x * Δx + ∂u/∂t * Δt.
Step-by-step explanation:
The formula for increments in the function u=f(x,t) is Δu = ∂u/∂x * Δx + ∂u/∂t * Δt. This formula represents the change in the function u when there is a change in both the position x and time t. The ∂u/∂x and ∂u/∂t represent the partial derivatives of the function u with respect to x and t, respectively.