Compute the following indefinite integrals:

a$){\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}{e}^{-2x}-2e^x+e^{2}dx$

c$){\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{1}{3x^4}+se{c}^2(x)dx$

b$){\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{3t^5-2t^3+t^2}{t^2}dt$

d$){\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{2}{\sqrt[\phantom{2}]{9-9x^2}}dx$