2017 · Q59
If D is the number of degrees and R is the number of radians in an angle θ , then which one of the following is correct ?
Elementary MathematicsTrigonometry
- Aπ D=180R
- Bπ D=90R
- Cπ R=180D
- Dπ R=90D
Explanation
This tests degree–radian conversion. D degrees and R radians describe the same angle θ, and 180° = π radians, so D/180 = R/π, i.e. πD = 180R. Option (c) πR = 180D inverts the relation — dimensionally it equates the two units the wrong way round. Hence option (a).