f(x) = x^2 and Pn ={0,1/n,2/n,3/n,...,1}. Compute L(f,Pn) and U(f,Pn)

thank you

Because $x^2$ is a increasing function on $[0,1]$ a lower sum is a left-hand sum:$\sum\limits_{k = 0}^{N - 1} {{{\left( {\frac{k}{N}} \right)}^2}\left( {\frac{1}{N}} \right)}$