Exercises. Evaluate the following integrals:

$($a$){\displaystyle \underset{0}{\overset{1}{}}}{x}^{2}dx($using right endpoints$)$

$($b$){\displaystyle \underset{1}{\overset{3}{}}}(2x^2+x)dx($using left endpoints$)$

Do not use the Fundamental Theorem of Calculus.