Article

Does plane angle have both, unit and dimension formula?

"No" it is has only unit (radian) not DF

Approach-

Step 1. formula-   plane angle is the ratio of the lenth of arc and the radius of the circle of which the arc is a part

Step 2. DF of each paramter in the formula, as arc and radius both are a type of length or in other words "both" have dimention of length so their ratio becomes dimensionless.