find the value of

a)$\displaystyle A \approx \sum_{k = 1}^{n} f(x_{k}^*) \Delta x$

b)max $\displaystyle \Delta{x_{k}} $

f(x)=x+1; a=0,b=4; n=3;

$\displaystyle Deltax_1=1,\ Deltax_2=1,\ Deltax_3=2\$

$\displaystyle {x_{1}^*}=1/3,\ {x_{2}^*}=3/2,\ {x_{3}^*}=3$