[填空题]
Let $z_1$ =2$\sqrt{3} cis( $\frac{7π}{12}$), $z_3$=2cisθ, and $z_2$=$z_1$+$z_3$ be represented by the points
A, B and C on an Argand diagram as shown below.
The shape OABC is a rectangle.
1.Show that θ= $\frac{π}{12}$.
2.Find arg($z_1$-$z_2$)=-$\frac{xπ}{y}$, x= ,y= .
3.Express $z_2$ in modulus-argument form.$z_2$=xcis($\frac{yΠ}{z}$),x= ,y= ,z= .
