Evaluate the definite integrals:

a$.{\displaystyle \underset{1}{\overset{6}{}}}\frac{1}{x^2}dx$

b$.{\displaystyle \underset{0}{\overset{1}{}}}{x}^3-x-e^x+2dx$

c$.{\displaystyle \underset{0}{\overset{\frac{}{6}}{}}}2sin(x)-4cos(x)-dx$