### Home > PC3 > Chapter 11 > Lesson 11.2.4 > Problem11-131

11-131.

COMPLEX NUMBERS: STANDARD $⇔$ POLAR

1. Rewrite the following complex number in polar form: $−2 − 9i$

Graph the point $(−2, −9)$. Then create a right triangle with the x-axis.
The hypotenuse of the triangle is the radius. Use the tangent ratio to determine the angle.

2. Rewrite the following complex number in standard form: $9(\cos(\frac { 5 \pi } { 8 }) + i \sin(\frac { 5 \pi } { 8 }))$

Use the half-angle identity for cosine or a calculator to compute $\cos(5π/8)$.