Trigonometric form
In trigonometric form you write a complex number as
z = r (cos φ + i sin φ)
Explanation
The point (a, b) is the affix of the complex number z = a + bi. So it applies
a = r · cos α
b = r · sin α
where r is the modulus of z and α is the argument. It follows that
Sometimes the notation cis α is used for cos α + i sin α.