A Change in variable is a term used to express the diffeence between 2 variables . Let $\Delta$ represents Change in 2 variables $x_{0}$ and $x$ then

- $\Delta x=x-x_{0}$
- $x=x_{0}+\Delta x$

If there is a function $f(x)$ such that when $x$ change by an amount $\Delta x$ the change in function will be

- $\Delta f(x)=f(x)-f(x_{0})$
- $f(x)=f(x_{0})+\Delta f(x)$

There are 2 points (1,3) (5,7) then

- $\Delta x=x-x_{0}=5-1=4$
- $\Delta f(x)=7-3=4$