${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}si{n}^2(\frac{x}{3}dx)$

a$)\frac{1}{4}si{n}^4(\frac{x}{3})c$

b$)3cos(\frac{x}{3})c$

c$)-3cos(\frac{x}{3})co{s}^3(\frac{x}{3})c$

d$)3cos(\frac{x}{3})-co{s}^3(\frac{x}{3})c$