The conversion between arc system and angle system is:

π radian (π is π)= 180 angle.

So it is 1 radian after conversion, which is about equal to 57.30 angle.

So tan( 1.5)=tan(57.30 angle * 1.5).

Attachment: Representation of radian and angle:

If you write numbers directly, it is radian. For example, 1 is 1 radian.

If there is a small circle on the upper right of the number, it indicates the angle.