Trigonometric functions (complex) I have to find $sen^3{5a}$ and $cos^2{5a}$ considering that $sen{a}=\displaystyle\frac{1}{2}$ and $a$ belong to the first positive quadrant. I tried to apply De Moivre formula to find $sen^3{z}$ and $cos^2{z}$ (I guess that somehow i can relate with $a$) but i don't know how to relate it with $sen{a}=\displaystyle\frac{1}{2}$

$$\sin a=\frac12=\sin\frac\pi6\implies a=n\pi+(-1)^n\frac\pi6$$ where $n$ is any integer

As "a belong to the first positive quadrant," $\displaystyle a=\frac\pi6$ (setting $n=0$)