 
 <prompt> text: ```Radian na di standard unit wey dem dey use measure angle for mathematics. Di length of an arc of a unit circle dey equal to di measurement in radians of di angle wey e get; one radian dey just under 57.3 degrees. Di unit bin dey part of SI supplementary unit before, but dem abolish am for 1995 and now radian dey considered as SI derived unit.

Separately, di SI unit wey dem dey use measure solid angle na steradian.

Radian dey represented by di symbol rad. Another symbol fit be , di superscript letter c (for "circular measure"), di letter r, or a superscript , but dem no dey use these symbols often because e fit easily confuse with degree symbol (°) or radius (r). So, for example, if dem talk say value na 1.2 radians, e fit be written as 1.2 rad, 1.2 r, 1.2, or 1.2.

Radian describe di plane angle wey dey subtended by circular arc as di length of di arc divided by di radius of di arc. One radian na di angle wey dey subtended for di center of a circle by an arc wey equal to di length of di radius of di circle. Generally, di magnitude in radians of such a subtended angle dey equal to di ratio of di arc length to di radius of di circle; that is, , where "θ" na di subtended angle in radians, "s" na arc length, and "r" na radius. Conversely, di length of di enclosed arc dey equal to di radius multiplied by di magnitude of di angle in radians; that is, .

Answer dis series of questions:

1. Which symbol dey represent radian?
2. Any other symbols dey?
3. Dem dey use am often?
4. Why?
5. Wetin di term dey describe?
6. Dem dey use am for many areas?
7. Wetin dey equal to di measurement in radians?
8. Wetin be di former classification of di unit?
9. E still dey exist?
10. Wetin happen to am?
11. When?
12. Wetin be di category wey e dey now?
13. Wetin be steradian?``` <response>: ```1. rad.
2. yes
3. no
4. but these symbols are infrequently used as e fit easily confuse with degree symbol (°) or radius (r
5. the plane angle wey dey under circular arc
6. yes
7. The length of an arc of a unit circle
8. an SI supplementary unit
9. no
10. e don cancel
11. 1995
12. an SI derived unit.
13. the SI unit of solid angle measurement``` 