`12i` Write the trigonometric form of the number.

The trigonometric form of a nonzero complex number is

`r*(cos theta +i*sin theta),`

where `rgt0` is the absolute value of a number and `theta in [0,2pi)` is the argument.

For this number the absolute value is obviously 12. Also this number lies on the positive half of the y-axis, therefore `theta=pi/2.`

The answer: `12i=12(cos(pi/2)+i*sin(pi/2)).`